I have a DPMS A15 A2 Lite 16", I got it on a trade about eight years ago, I have less that $600 in it, a case and four magazines. I was issued, Colt M-16a1's in the Army. Other than that, I hadn't had much experience with different manufactures. In the 80s and 90s I used a semi-auto Galil ARM and HK91 as my own personal military type rifles. I fired hundreds of rounds without a problem through my DPMS, before I ever learned on the internet that they were sud-standard. I've checked mine now and for what its worth, my example has M-4 feed ramps, staked gas key, and 5.56 chamber. It also has shown no signs of problems. I really would prefer an A3 upper, but I do okay with aperture sights and looking over the top of the front sight post at short range(less than 50 meters), not the best, but it works for me.
All I can do though, is relay my limited experience with one example. If others with lots and lots of AR experience say they have seen certain DPMS rifles that were out of spec, or failed in high volume fire, I have no reason, or bases to doubt them. If shooting rifle courses that require 3000 rounds in a day, or a weekend are on the agenda, then buying a more expensive rifle, of higher quality is obviously the thing to do.