I looked into POF when they first came out, did some research asked questions and in the end decided to pass.
Some gen1 POF owners have nothing but good things to say about them wile others have nothing but complaints. Overall the general consensus at the moment on POF is not good. You either have a good or bad one.
I just took my POF p-415 out again, and I gotta say that it's a really smooth rifle. It's a ton of fun to shoot and so easy to clean. It's not too different from my AK type rifles cleaningwise. I just wish that .223 ammo prices would drop! I also wish more companies made gas piston AR's to lower the price.
I took out my P.O.F. p415 (HK 416 clone) with Barska Electro Sight red dot optic. The red dot sight works pretty well, and is sighted in at about 25 yards. I used PMC 55 grain ammo and got pretty good results. I really like my P.O.F. p415. It's accurate, easily modified, a bit on the heavy side, but really a great rifle.
It has an "18 heavy barrel and a great HK style front sight. I use a Stag Arms lower with the POF upper and I've had good luck with just about all the mags I've used. I bought some Tapco mags for $10 a piece and they work great so far. I really like the Korean HK 416 knock-off magazines as well. The POF p415 upper is a bit pricey, but if you want quality and accuracy, POF is the way to go. If I had the money, I'd like to get one of their 7.62x51 (.308) models.