TheYankeeMarshal did a disassembly video on the APX and it was a disaster. See for yourself. Hickok45 loved the 509 so much he bought one. I handled both the APX and the 509. I like the APX a lot but the takedown seems to be cumbersome. I'm partial to FN in general...I have an FNS 40, and the trigger seems to be the same as the one on the 509. Pretty good triggers, but they can vary in roughness with the reset. The 509 I handled had a very coarse reset that was very sticky. Probably not that way across the board, and with use should smooth out.
Edit - Also, if he is a collector, the APX and the 509 were in direct competition with the P320 for the DoD contract. If you want the best one out of the contract competition group, I might go for the P320...maybe.