Fair enough. I've had a sample of 6 BCM Carbines in my family with the only person I know having an malfunction was me (stuck case when shooting Wolf after about 500-600 rounds) and two issues with green follower .44 MAG cheap magazines; the cartridges were released early into the top of the receiver and pushed the bullet into the cartridge (I put magpul ATF followers in and I've never had an issue since).
I had a Sionics lower with an A5 extension with the A5H2 buffer and a BCM Midlength upper and 16'' barrel that had two Failures to Eject; I was testing that before Form 1-ing it. I was so concerned I bought another BCM lower, shot about 50-100 rounds through it and Form 1'd that lower.
But, I had a family member tighten down a receiver extension after replacing the end plate with a Magpul ASAP plate; the receiver eventually worked loose and began to rotate freely. It appears he didn't re-install it properly.
Which... kind of highlights my concern.
YMMV. I'd vouch for BCM.
God Bless,
Brandon