Piepaned,
Well, you pretty much know my feelings about POF's product. I'm a big fan of their systems and I completely agree that when you consider the hardchromed bolt, carrier, gas block plug, and the entire plated upper receiver, I think they are the best value for the money. In fact, the M4 that is pictured in my avatar and on the Downrange TV video section is my POF M4 Upper with the standard handguards. It served me very well.
What I will say about Piston driven systems in general is that I would stick with a dedicated system (POF, LWRC, etc.) and not a retro-fit kit. I have no experiences with the retro-fit kits so this is purely my uneducated opinion, but I would wait for a while before I paid money for a retro-fit kit. I want to see how some of them perform over the long haul. I would like to see how the kits are holding up after 10,000 rds. of hard use, etc. I'm sure the various companies do extensive testing, but I put my faith in the bubba brigade method of testing. If the system can survive a couple of years with Bubba, then I'll start the looking into purchasing one.
USSA-1