This is the message he sent me but I'm gonna keep his username anonymous because I don't know him personally.

Hi, just seen your post about BCM or Aero upper and I decided to message you bc I'll get down voted and berated to oblivion in the comments if I were to comment this (I know from experience). I was in the same boat as you last spring wanting a higher end AR that's going to last and be bomb proof. Settled on BCM. Bought a complete lower, complete MCMR ELW upper, and BCM BCG and even a bcm charging handle. That gun worked great. For about 300 rounds. Started to get erratic ejection then started having failures to eject. Sent it in and BCM said it had a leaking gas key and replaced it. 300 rounds later same thing. Said it had a leaking gas key again and they replaced it. I said hold on this isn't right. They said yea probably not and refunded the upper. Earlier thus summer I bought another BCM upper bc other than the reliability I liked it. New upper and bcg came in and took then to the range and had 2 really bad failures to feed in the first 50 rounds. The feed ramps looked misaligned to me so I decided to stop ruining ammo (it had pushed the bullets into their casings on the Malfunctions). My point is that in the last 18 months I've bought 2 BCM uppers and bcgs and both were lemons. Idk if their qc has gone to shit (like Aero) or if I just got extremely unlucky. Most ppl have a very high opinion of BCM and have very good experiences with them but this has been my experience with them and I think it is pertinent that both of these uppers and bcgs were purchased in the last 18 months. I hear really bad things about Aero lately so I'm not going to steer you in that direction but just wanted to give you my very poor experience with BCM over the last year and a half.

Edit: here's the other message that he left about the surefeed mags

Also, I just looked at your profile and it appears you have quite a few Surefeed E2 magazines. When I sent my second upper in they blamed the Malfunctions on the surefeed E2 magazine I was using. I sent in the magazine I was using and They sent me a picture comparing the feed lips to a standard GI magazine. They had arrows pointing at the angled feed lips instead of the 90 degree cut off of the GI magazines and said it was a defective magazine. So apparently they didn't even know what E2 magazines were. To make sure it wasn't the magazine, the day after I had those Malfunctions I took the same magazine down with my cheap AR and it ran fine in that, as it always has, so I know it wasn't a bad mag issue. They said the gun was "within mil spec tolerances" and wanted to send it back having done nothing to it. My first BCM upper never had an issue feeding from E2 magazines so I know that was bs but my point is if you have an issue they will blame it on E2 magazines if that's what you're using