Like many, when I’m abroad I use the hotel wi-fi (if there is no charge); I buy a local SIM card; or I don’t bother and just roam with my home network.

But during my last trip I spent three weeks in Greece using Mi-Fi and a SIM card from Cellhire and I am now a convert.

Firstly, what is Mi-Fi?

It stands for mobile wi-fi. It’s a small gadget as per the pic above, like one of those small mobile phones circa 2005, and works as a mobile router.

It takes a SIM card inside. Mine was from Cellhire, valid for the whole of Europe, for 30 days and 10Gb.

The beauty of Mi-Fi as I see it, is that, as it works as a router, you can connect more than one device. I connected both my laptop and my UK mobile so you can see immediately how you save money. In previous trips I used a dongle and local SIM for my laptop and roamed using my UK mobile provider.

There are more advantages: the Mi-Fi connection is encrypted; Cellhire gives you a 4G gadget; and the Europe card is not tied to an operator so it picks up the strongest signal where you live.

So in theory, you have better coverage than locals who can only use one network.

In Greece I’ve always used a COSMOTE SIM card for my laptop. My Mi-Fi spotted that in that particular area Vodafone Greece had a stronger signal than COSMOTE and connected to that. The speed improvement was a revelation.

The gadget I rented was a Huawei E5377 Ts-32 Wireless Modem (£105 on Amazon) that is fully portable so it can lie on the beach with you or you can take it on a hike.

The battery data seem too good to me (coz they also count it being on standby) but you should get at least six or eight hours out of it with a download speed up to 150 Mbps and upload speed up to 50 Mbps.

It connects up to 10 devices so if you are a family with children and each one has their own smartphone paying charges in the UK, then it’s more than worth it.

The convenience is magnified if you consider local laws.

In many countries you have to register with a passport to even buy a local SIM, like Greece, South Africa or Singapore.

In Brazil you have to register the same SIM in every state you visit which is a pain if you’re travelling for four weeks like me in Rio state, São Paulo state, the states of Bahia and Amazonas, dipping your toe for a day or two in Minas Gerias.

In Germany you have to sign your life away just to get to the hotel wi-fi, in case you download something that is covered by Germany’s frightening copyright laws.

No such problems with renting a SIM from the UK.

Is the setup easy? This was the revelation: it works almost like a GPS. You turn it on, wait and that’s it.

I understand that if you buy your own Mi-Fi and put in a SIM yourself there is some fiddling with an interface on your laptop or mobile, but I didn’t have to do any of that.

Is the hire easy? Yes, it comes by UPS courier with a return bag and prepaid postage.If you are homebound, just call the number on the returns instructions and a courier will pick it up from your current location. It’s easier to just hand it in at a UPS outlet in your area.

Cost? This is where economies of scale become important.

If you have one device with a UK Mobile provider and pay something like £1.99 a day and you go for a week, then it’s not worth bothering.

But if you are going abroad for two weeks and have two items (a laptop and a phone) or you are a family with teens who have their own phones, then you’ll save a lot.

I used Cellhire’s SIM card that’s available via its Europe-wide  offering: 10GB for £89.99 or 1GB for £39.99.

Prices are for 30-day hire slots. For rental of a 3G Mi Fi, add £10.00; for a 4G Mi Fi, add £19.00.

There are many packages for individual countries: eg Spain 10GB – £39.99, Germany 10GB – £39.99, Italy 10GB – £66.99, France 3GB – £29.99 and France 6GB – £46.99.

Regular travellers could buy a Mi Fi from a supplier and then just rent the necessary SIM and data bundle for the country they are visiting.

So do your calculations for your own circumstances.

I have devised a rule of four: if it’s four of you for a week abroad each with one device, or one of you going for four weeks with one device or two of you going for two weeks or more with two devices, then it’s worth renting.

A family of four with four devices caravanning in France for two weeks would spend a basic £1.99/day * 4 smartphones * 15days= £119.40 minimum with O2 versus £29.99+hire. Vodafone is even more expensive.

If you travel on InterRail for a month and cross several countries it’s £1.99*28 days = £55.72 v £39.99 plus hire. I assume you won’t be downloading movies or listening to Spotify on holiday, because if you do you need to pay extra on  your mobile provider and go on a higher package Mi-Fi.

In Greece, where I write guidebooks for the Rough Guides and stay for weeks upon weeks, I use a dongle with a local SIM for COSMOTE for my laptop (about £15 for 10 days, 3GB plus the dongle for £50) and O2 (£1.99/day on my smartphone).

I stayed for 21 days in December so the cost would have been £1.99*21=41.79 plus 2*£15 days hire=£30.  Or £72 minimum, with no encryption. This vs £39.99 plus the Mi-Fi rental. And what price that faster connection?

You can of course use this Europe-wide SIM in the UK as an extra data bundle for any remaining days after you return.

Disclosure: I was given the Mi-Fi free to check it out, but I’ve been completely sold on the concept and I’ve been recommending it privately as well.