Mike,
I've a lot of satellite and TV experience over here, stretching back almost 25 years. I'd strongly suggest that you get your Humax Freesat in the UK, primarily because you're not very likely to find the real Freesat version in France. (You can, however, buy your Humax Freesat from Amazon in the UK & they'll deliver it to France for very little extra.)
The first difference is that genuine Freesat receivers are automatically managed by the Freesat consortium 'over the air'. This covers adding new channels and changing frequencies, when necessary, for existing ones. The second difference is that the genuine receivers have the full Electronic Programme Guide (EPG) showing up to seven days ahead. Most non-Freesat receivers can only tell you what's on 'now & next'. A further issue I've had trouble with on some non-Freesat systems is that they don't seem to be able to cope with Channel5, whereas that's automatically part of Freesat.
You can, of course, just buy any Free-to-air receiver, from Humax or anybody else, & set it up yourself. They are, however, often a bit out-of-date so far as the frequencies are concerned, even when they're new. From then on, you need to manually make the changes that Freesat does automatically for you. Doing this varies in complexity from model to model, but, IMHO, is best simply avoided by going Freesat in the first place. There's no significant price difference if you compare receivers of similar quality. You can actually buy some quite cheap Freesat receivers, in the UK & from Amazon, but I've had nothing but trouble with them. (I've not tried the Openbox, so can't honestly comment on that one.)