Don't have a FPC and don't plan to buy one, but I have owned a number of PCCs, and for fun, ergonomics, and with a bit of time, the FX9 has become, hands-down, my favourite PCC.
Agree with the other poster about running it wet, but not too wet. It comes bone dry, so lube it up before using it. Also absolutely agree with how dirty it gets. After even a box of 50 rounds, there's always not just the typical powdered carbon build up, but there is some gritty, grainy sediment type of carbon build-up. I have to clean it often and keep it oiled.
You will probably not find a better gun for ease of takedown. I can get the bolt out, and firing pin and spring out in 15 seconds or less. With just a punch or something relatively pointy to push the retaining pin out (I only need to take out 1 of 2).
Controls are superb. Everything is where your fingers think they should be. Weight is OK, far better balance than my PC Carbine (aluminum handguard version).
I am not a trigger guy, but I found the trigger to be totally fine, albeit slightly heavy (I never upgrade the triggers on my guns, so just getting used to it).
The charging handle is very small, even on my latest generation "enhanced charging handle" model. I have small hands, and notice the charging handle could be larger - I can't imagine what those with beefy hands think. And I can't imagine how small the original handle was. There is a guy here who sells third party larger charging handles that he makes, but I am cheap and can't be bothered to drop the cash for that.
I have a Holosun HS515GM mated with a Holosun HM3X magnifier. Also have a Magpul angled foregrip on it, along with a Streamlight Pro Tac HLX on it, all of which adds some weight to it, but it's still manageable.
For ammo pickiness, you will need to try different kinds. It suggests that you use 115gr FMJ (from certain brands for some reason) for the initial use times. I wrote to FO and asked them how many rounds is this "break in period". They said it is not really a break in period and they didn't call it a break in period. What they DO NOT recommend is aluminum cased ammo. So I have just used brass cased.
For weights/performance, you'll have to try different ones. Mine seemed to settle well with 147gr. but your mileage may differ.
Also for hollow points - better try some and out of different mags too. Mine does not like Critical Duty (FTF issues), but is OK with Gold Dots, and mostly OK with HSTs.
Accuracy is nothing to write home about. This is not a precision rifle or carbine. More of a plinking, fun gun, but it's not bad accuracy either. Depends on your ammo and of course the skill of the shooter (for which I have none)
I did have an issue with me with the last round bolt hold open getting progressively unreliable to the point it didn't work for 90% of the time. Then the bolt catch/release went off by itself when the gun wasn't even touched...that was more annoying than anything else. Once I found out there was a lifetime warranty on these things, I opened up an RMA with Wolverine, sent mine back, they did something to better mate some parts (I can tell, as the bolt catch is only slightly a hairline wee bit off center), and now it runs like butter. Bolt catch/release never goes off by itself and last round bolt hold open works 100%.