I've used their 5.56mm uppers, lowers and parts on multiple builds, and I have been very pleased. I think they are one of the best values around in AR parts, and they are usually the first place I look or send people to look who are interested in building one. The only downside to PSA is that their shipping times, especially on sales items, can be slow. If you order an upper or a kit that is on sale, expect it to take 3 weeks before it ships. Personally, that has never been an issue to me, because I've never built an AR that I had to have overnight, but it is something you should be aware of. I did have them leave one part out of an LPK, but they quickly shipped me the missing part after a phone call. I would like to build one of their AR-10's.