Hi Caran.
This isn't really my specialist area. (I didn't even have a smartphone until a few months ago, so I'm no expert on mobile technologies).
However, as I see it, that device is really only a 'posh dongle', which is specifically designed to work with the 'improved' version of 4G, known as 'LTE-A'. Given that LTE-A isn't that widely available in the UK yet (and probably not in France either) I'm not sure that it would really give you anything that a standard 4G dongle wouldn't.
If you can get a decent signal on your mobile phone (and you're on a tariff that's not too expensive for data) then it would probably make most sense to either:
(a) use your phone directly for internet access (rather than your iPad) ; or
(b) turn your phone into a mobile hotspot (so that it acts like the router in your home) and connect your iPad to it via WiFi:
https://support.google.com/nexus/answer/2812516?hl=en-GB