Mobile Wi-Fi, or MiFi, comes in the form of a portable Wi-FI router that allows you to connect multiple Wi-Fi devices to a single 4G data SIM in a router and get online wherever you go. That includes smartphones, tablets and laptops and they're particularly handy when travelling.
Here are the best mobile Wi-Fi hotspots and portable wi-fi routers you can buy.
Your buying guide for the best mobile Wi-Fi in 2018
If it's still a little confusing, here are some of the benefits of getting a mobile Wi-Fi hotspot.
You can connect multiple devices: Some MiFi devices let you connect 10 or more devices to a single hotspot, which will work out a lot cheaper than paying for a mobile data plan for each of those devices.
You can connect Wi-Fi-only devices to a mobile data connection: Tablets are great to use at home, but what about on the train, on the beach or by the pool? Wherever you can get a phone signal, you can use MiFi to create a wireless network and get online from any Wi-Fi device.
You can save money on your next tablet: Buying a tablet with a 4G data connection adds around £100 to the price, and that's before you consider the monthly fee for your data. Use some of that money to buy a MiFi router instead and you'll never need to buy a 4G tablet again, nor base your purchasing decision on whether a cellular option is available.
You can reduce roaming charges: Most mobile operators offer free roaming in the EU, but fixed-fee roaming elsewhere, allowing you to take your home tariff with you for a set cost. Rather than paying this extra charge on all your devices, turn off data roaming on them and connect them all to a mobile hotspot. You'll pay this charge only once, but get all your devices online.
You can avoid using slow hotel Wi-Fi: In a similar vein, for those hotels that still charge for Wi-Fi, you can get the kids online all day and at a lower cost than what the hotel would charge. Better still, you can avoid using the same network as all the other guests, which is usually slow and often has poor signal in your hotel room.
You can add 4G connectivity to a 3G device: If you're still using a phone that doesn't support 4G networks (which often use different frequencies abroad), MiFi allows you to speed up your mobile internet connection.
You can get faster download speeds: Even if your device already supports 4G, you could potentially get faster download and upload speeds by switching to a MiFi that supports a faster connection.
You can share storage across your own mobile network: If your MiFi supports a microSD card, you can share that storage across all your devices, which is especially handy if they don't support expandable storage themselves.
How do I choose a mobile router?
When it comes to choosing a MiFi device, you have three options:
1. You can get a free or low-price router from a mobile operator in return for a fixed monthly subscription
2. You can buy a network-unlocked router to which you add a data-only SIM of your choice, with much lower monthly payments
Many people will automatically go to their mobile operator for a MiFi device, since it's an easy solution and you don't need to pay anything up front. But this isn't always the best idea.
If you buy a MiFi router from a mobile operator it will be locked to that network, preventing you from shopping around for the best data deal. You will also most likely pay over the odds if you choose to pay nothing up front but tie yourself into a two-year contract.
For example, EE's 4GEE Mini with 30GB of data is available for free on a £20-per-month two-year plan. Over the two years you'll pay £480.
By comparison, if you buy the mobile router yourself (most are between £50 and £100), you can get a data-only SIM with 40GB of data - even more than EE's plan - from as little as £16 per month from Three. Over the two years you'll pay only £384 for your data - but potentially a lot less if you don't need that much data, as there's a range of cheaper plans available too.
Better still, you can subscribe to a rolling monthly contract, allowing you to move on at any time with only 30 days' notice - though the monthly cost will likely be higher.
All UK mobile operators supply MiFi devices, but remember that not all routers are created equal and the one supplied by your mobile operator may not be the best.
TP-Link M7350 4G Mobile Router
TP-Link's M7350 is a solid mobile router than has the big benefit of being network-unlocked. That means although you'll pay in full upfront, you can choose any data deal from any UK network operator, and you aren't tied to a contract.
The TP-Link supports all three UK 4G LTE bands, with up to 150Mbps download speeds and 50Mbps uploads. It can create a wireless network for up to 10 devices, and supports a microSD card for shared storage and has an LCD that tells you the signal strength, how many devices are connected, how much data you have used of your total limit, plus the remaining battery capacity.
You can also use the LCD to cycle through a menu that caters to such options as toggling on or off data roaming, switching between 2.4- and 5GHz output, and choosing between 4G, 3G or a mixture of both.
A final option displays a QR code that takes you directly to Google Play or the App Store to download the tpMiFi app, which lets you manage users, alter the range, share files and read text messages.
The TP-Link's 2550mAh battery should be good for up to 10 hours of 4G connectivity, but lasts days on standby.
Most of the options in this chart are suitable for those who will regularly need the use of a mobile Wi-Fi router, but MyWebspot is more appropriate for those who have a one-off requirement. If you're going on holiday abroad (potentially outside the realms of free roaming in Europe) and have several devices to get online, the service allows you to hire a hotspot for use by up to five devices in more than 100 countries.
Daily charges might sound steep at first, starting at €7.90/£7.12/$9.16 per day, but that's nothing compared to what your mobile operator will charge you once you overstep your data allowance. It can also be very expensive to connect to the Wi-Fi provided by resorts, which is often slow and time-limited.
The data allowances are also very generous. You can get up to 10GB unrestricted usage in parts of Europe, and 5GB in the US (per day). After this it cuts down to an almost unusable 256kbps, so it's not quite 'unlimited' but as good as.
The router itself is the same as that offered by GlocalMe (covered further down this page), but setup couldn't be simpler. The device can be delivered directly to your resort (or home if you prefer), then you turn it on, wait a moment for it to connect to a local 4G LTE network, and pick it up on your mobile device as you would any other Wi-Fi network using the SSID and password printed on the label on the back. On your way home you pop it in the post box using the prepaid envelope.
MyWebspot claims download speeds up to 100Mbps, and uploads of up to 40Mbps. In our testing in Lake Garda, Italy, we recorded an average download speed of 33.5Mbps, and upload speed of 26.8Mbps. Naturally these speeds will decrease as you add multiple devices.
You'll get about eight hours battery life from the Mi-Fi router, which is supplied with the appropriate local charger for your holiday destination.
There's no companion app, which means even technophobes will get along with MyWebspot, though it would be handy to have some way of monitoring usage across multiple devices given that there's no LCD screen.
In case the slightly larger model number didn't give it away, the TP-Link M7450 is a more recent and advanced version of the M7350. So why have we ranked it lower on the chart? Simple: at the time of writing it's about double the price, and we're not sure that most people will see enough benefit to justify the extra expenditure.
Like the M7350, it's sold unlocked and should work with any major network, either in the UK or abroad. It supports cat6 LTE, with 300Mbps downloads (double the M7350) and 50Mbps downloads; you can pick between either the 2.4GHz or 5GHz Wi-Fi bands; and you can connect up to 32 devices simultaneously - way, way more than most people will ever need.
Menu navigation is simple, and the clean UI makes the most of the two buttons and small screen to give you the info you need. For more complex setup - including USSD support, useful for connecting to many foreign networks - you can use either the web portal or free smartphone app.
The 3000mAh battery should give you an impressive 15 hours of working battery time, though we haven't tested that limit ourselves. Oh, and you even get a microSD slot, which supports cards up to 32GB and can be used as a quick way to share files between devices.
The Skyroam Solis is a neat little Mi-Fi router that's interesting for two reasons (beyond that vibrant paint job): its cloud-SIM functionality and built-in power bank.
You can connect up to 5 devices at a time, and the Solis works in over 130 countries thanks to partnerships with more than 300 different carriers - so you can expect a solid 4G LTE connection just about anywhere you go. Because it uses a cloud-SIM, there's no need for a physical SIM card, and no need to sign up with a specific carrier.
The official accompanying app lets you check which devices are connected to your hotspot, keep an eye on your data usage, and buy more data as and when you need it. It's bright, clear, and easy to use, even for the non-technically minded.
Skroam promises 16+ hours of battery - we saw more like 12, with two devices connected all day, but that's still very impressive. Even better, the 6200mAh battery doubles as a power bank, so if you don't mind sacrificing a bit of Wi-Fi battery life you can keep your phone or another device topped up when you need it.
There's also a lot of flexibility in how you pay, with Skyroam offering a few different payment options. First up, if you only want to use it for a single short trip you might want to rent it, which costs £9/$9.95 for unlimited Wi-Fi - though speeds drop after you use up 500MB.
You can also buy the device itself for £135/$149.99 and access the same daily unlimited plan - just £7/$9 per day if you own the device - or get monthly unlimited data for £79/$99, though this is a limited time offer.
Finally, Skyroam also offers a much cheaper monthly plan called GoData. Again, you'll need to buy the hardware first, but it's then £7/$9 per month for 1GB of data, with each subsequent GB costing another £7/$9. There's also a cheaper bundle offer if you buy the Solis and commit to the plan for a full year.
O2 4G Pocket Hotspot Plus
O2's Huawei 4G Pocket Hotspot Plus offers staggering battery life with up to 500 hours on standby, and you can use it to charge up your phone when you're running out of juice using the built-in Micro-USB cable.
It also supports microSD cards, allowing you to share storage between connected devices. A built-in LCD shows useful stats such as signal strength and battery life.
Data charges can be a little expensive, but O2 has a handy tool that lets you customise your package, changing your data allowance, contract length, and upfront cost to find the plan that best suits you. You can also buy it for £77 on a PAYG basis.
The GlocalMe U2 is best suited to frequent travellers who want to quickly and cheaply get online anywhere in the world, but it's a useful device for back home too, especially for business users who are tired of dealing with flaky internet connections while commuting.
With embedded encryption the U2 also presents a safer method of getting online than connecting to potentially vulnerable public Wi-Fi hotspots.
It's able to work as a standard Mi-Fi device, sharing the data connection of a mobile SIM (the network-unlocked Glocal U2 accepts both full-size and Micro-SIMs) with up to five devices, and has cloud-SIM functionality. You don't need to insert a local SIM in this mobile router in order to get online in over 100 countries - you simply put some PAYG credit on it or buy a data pack and away you go.
GlocalMe works with multiple network operators including AT&T, Sprint, Verizon, Orange, China Mobile, Vodafone, T-Mobile, O2, China Telecom and China Unicom, and supports a wide range of connectivity bands. Because it will automatically connect to the best network wherever you are, you'll often find - as we did - that getting online via the U2 is faster than with your current SIM.
Most data packages last 30 days, and the U2 itself can keep going for up to 12 hours on a single charge, which should easily power you through any working day. When the 3,500mAh battery runs down charging is fast (around 3.5 hours) over a 3A Micro-USB connection.
Three Huawei E5573
Then there's the Huawei E5573 from Three. It supports up to 150Mbps download speeds and 50Mbps uploads. As with the 3G MiFi you can connect it to 10 devices.
Prices start from £9 per month with 2GB of data on a two-year plan, or you can get up to 40GB for £18 per month on a two-year plan.
A huge benefit of buying from Three is that if you're going abroad Three's Feel At Home policy lets you connect to the web with no roaming charges in several foreign destinations.
EE 4GEE WiFi Mini
EE's 4GEE WiFi Mini is a good-looking MiFi that comes with three interchangeable colour bands and a cloth pouch. It lets you connect up to 10 devices at once, and has a 1500mAh battery inside for up to 50 hours battery life on standby.
One benefit of buying from EE is the decent-value data allowances and 'double-speed 4GEE' fast network. However, don't be fooled by the 100MB of free EU data per month - you'll quickly whizz through that when using the Mini abroad.
Several plans are available for the Mini, and EE recommends the £20-per-month 30GB plan for which you pay nothing up front, but it goes up as high as 50GB for £40 each month.
The E5330 is a basic MiFi that supports only a 3G network, but if you can't access 4G where you live then it might appeal. It used to be sold by Three, but now you can only buy it through Amazon - but at least that means it's unlocked and can be used on any network.
It supports up to 10 devices at once, with six hours' usage and 300 hours' standby, but remember that download speeds will be lower than with other rivals.