I haven't shot a FN 5.7 pistol so I can't say how the recoil is so as far as self defense I don't know whether its recoil allows for faster follow up shots or not.
I lost interest in the pistol when I learned that the main feature of defeating bulletproof vests wasn't available to the general public via the restriction of sales of ammo. Without that it just seems like a .22 pistol with less capacity than the KelTec PMR. I don't know about ammo prices but I would think 5.7 ammo would be more expensive than .22 magnums. (ETA Although centerfire rounds are more reliable than rimfire)
So personally I would go with an XDm which in 40S&W has 16+1 rounds compared to the 20+1 of the FiveseveN.
There are many other good options though. :-) Check out the FNX line of pistols. I have a FNP-45 (they changed the name to FNX) and I carry 15+1 of .45acp!