According to the stats it's not just usable, it's popular - but not in English-speaking countries, presumably because three-syllable names tend to get shortened and the most obvious English shortening of
Florian would be Flory/Florrie. And I can't see that appealing to your average boy here much, unless he were a particularly, um, florid type of dude.
It's a nice enough sound though, and I do like it.