Mobile internet..? Options? French Network or UK?

Hi, wonder if anyone can advise.

We need to work in France in a fortnight and we won't have wifi installed yet; I need to work from my laptop and need a dongle - or even better; one of the cellular boxes that creates, in effect, a wifi signal that anyone can connect to, like this:
http://www.gloopy.co.uk/user-reviews/ee-osprey-pay...

Best to buy in France? If so, what's the best option for this? Any advice apprciated. I note that 'Three - here in the UK - do a dongle that you can use in France at no extra cost. It would be handy to buy in the UK but I'm not sure about Three as a network. We alreadyd have an EE box (as linked to above) that I need to check whether we can use.

Thanks for any tips.