Can't imagine wanting to carry the 5.7 for any sort of self-defense role, unless I worked on a ranch or something similar, in which case I wouldn't likely need to conceal it. Bigger pistol to conceal, too. I'm sure it could be done, though, especially for a larger than average person.
That said, I have rented the FN and it's a fun, fun gun to shoot. Nearly nonexistent recoil and you can dump the contents of its 20 round mag in a few heartbeats, accurately. I'd love to have one. I have read that the Ruger is an improvement in grip vis a vis the 5.7, and it certainly is a more appealing looking weapon, aesthetically.
Interesting to hear your thoughts on this pistol and why you'd desire to conceal it.