Hello !
If you are talking about “France obstacles and VFR landmarks” add-on, I’m using it for a while and it’s quite good. It add many elements likes bridges, castles, churches, observatories (at least the one in Pyrenees), antennas, gondolas, water towers, electric lines, etc… Keep in mind that this add-on have nothing to do with satelite imagery, and that this is mainly about french countryside, as it will have only few effect on big cities.
As far as I can tell, it replaces some vanilla buildings by new ones (like the castle in my birthplace for example) and some which are lacking in the original game (churches most of the time). it means that when world update 4 will be released, it could make conflicts with it, untill they release a new version of the add-on. If you bough some add-on dedicated to specific buildings like churches and castles, you could have conflicts too.
Regarding their website, it covers the whole country, so Corsica should be included (or they’ll have troubles with corsicans in anyway :p)
I hope I helped you, see you over french landscapes 