Mobile wi-fi, also called mi-fi, is a step up from a mobile broadband dongle. While a dongle can only connect one device with a compatible USB port at a time, mobile wi-fi can connect several devices at once: think of the broadband router sitting at home providing a wi-fi signal to all the devices within range. The mobile wi-fi devices shown above are basically very neat, portable routers, which use the mobile phone network to create a wi-fi hotspot.
A mobile wi-fi device can also help reduce the strain on the batteries of our other devices - providing a strong wi-fi signal for them to lock onto, rather than wasting power searching for and switching between the best signals from further afield. A mi-fi hotspot can also enable people with wi-fi calling on their phones to make calls where they might otherwise not be able to.
Most mobile wi-fi hotspots are sleek little things not much larger than a credit card - designed to fit neatly in a pocket or bag. They require a charged battery to work, so expect to get from four to six hours of use out of one between charges. As standard mi-fi devices recharge via a USB cable, it's possible to extend the battery time by plugging them in to a laptop - but bear in mind that'll affect the laptop's battery life too.
Some mobile wi-fi devices offer a slightly longer lasting solution, as long as there's access to a 12V power supply. These are the ones sold as "in-car" portable hotspots, and they plug into what would once have been the cigarette lighter in a car or vehicle. This means the power - if not the mobile broadband signal - will be guaranteed for the length of the journey.
Light users are likely to find a pay as you go mobile wi-fi deal better than a mi-fi contract, as will those who aren't sure how much data they'll use from month to month, and people who want to be sure of the best mobile wi-fi signal wherever they are. PAYG mobile wi-fi users can always upgrade to a contract if and when they want to, by getting a pay monthly data SIM further down the line.
The advantage of a pay monthly mobile wi-fi deal is that users don't have to worry about running out of data in the middle of something. But while they might get cheaper data as long as they stay within their allowance, the charges for going over that limit can be quite stiff - so it's just as well that people with mobile wi-fi contracts are also more likely to have access to their provider's public wi-fi network.
The speed of the connection users can get when using mobile wi-fi depends on a few factors, but most obviously we need to consider the strength and type of signal the mi-fi device can receive: 3G has the widest coverage, although it's slower; 4G is up to 2.5 times faster for downloading data and almost 3.75 times faster for uploads, but it's not as widely available. Most 4G mobile wi-fi devices will use the 3G network if there's no 4G signal available.
The best mobile wi-fi deal is therefore not necessarily the cheapest - it's the one that offers the best coverage at the best price, including when we're indoors or on the move. Most mobile networks provide fairly detailed coverage maps on their websites - and it's also worth checking with friends and colleagues to get an idea of what a network's data service - and customer service - are like.