The BCM Gunfighter CH's are awesome. I chose the medium latch (Mod4) and it doesn't seem to get in my way at all.
BCG shouldn't really be bought used. Second hand is fine if they are NIB. But once they are mated to a particular chamber, you shouldn't be switching. The reason I say this is that the secondary used market is a great source for BCG's right now.
I don't know why you wouldn't want to just go mil-spec from a reputable company. If you do, then you can go with a number of different sources.
.45acp, .40 S&W, 9mm, .38 Spl, .380 acp, 22lr
12 gauge, .223/5.56x45mm, 30-30 Winchester
2 Chron. 7:14 Christians must seek His face