Interesting.
I haven't tried the FNS, but I had an FNX a few months back and was somewhat disappointed. Even after a trip back to the factory and some spring changes it wouldn't function reliably with mild range-grade ammo. Definitely prefers full power duty ammo, which is what the factory said as well when they sent it back to me.
When it worked, it worked great. Very accurate and pointable. Felt good in the hand, but I didn't want to mess around with it any longer and didn't want to buy expensive duty ammo for plinking so I traded it away and went back to my Hi-Powers & Glocks, which have a hearty appetite for anything I feed them.