They pretty much all work the same (we are talking the major brands you listed). POF is a Billet lower, meaning it is CNC machined out of a solid chuck of aluminum. These type are more expensive.  Forged (most brands) are pounded into the shape of a lower then the "excess" is machined away. Cheaper lowers are not as pretty (not smoothed out as nice, grinding marks, etc) My Essential Arms function just as well as my RRA or Bushmaster lowers, they just aren't as pretty............but i don't care how pretty it is, as long as it works.  

 I would use any lower from a major brand if my life was on the line........it is the internal components that i WILL NOT get from a cheap supplier. It would be White Oak, Colt, RRA, or Bushmaster  for my internals. Yes, most are made by the same few companies, i just have seen that these companies have a very good quality control of what they sell.


Note: Hesse, Vulcan, Blackthorn, etc are NOT included.

 

Stag makes pretty good parts, IMO.