My wife has the FNX-9 and I have the FNX-45 - I'm still getting used to the FNX I've had the Glock 21 since 1999, but I liked my wife's so much that I decided to change too.
With the 9 I do have the occasional issue with cheap ammo. But we probably have a good 200 rounds of Speer Gold Dots with no issues, and our favorite practice ammo, Speer Lawman 115gr has never failed. It is just so hard to find the good stuff these days
Get to know your FNX. If you are cocked and locked, practice going from safe to not without decocking, I still can't do it 100 times in a row
. The FNX has some serious travel on the slide - more than any firearm I've ever owned. I think this is why my son had some limp wrist trouble early on.
Most importantly, enjoy your 18 rounds of 9mm firepower!