I also have the radial-delayed blowback system that I use CMMG's Endomag inserts specifically for, and they work absolutely great. But that's with the RDB where everything is pretty much where it wants to be in an AR design anyway. I really didn't have much interest in the 'regular' Endomags because I just couldn't see that plastic ejector holding up. I instead used a Stern Magwell adaptor (w/ Glock mags) for milspec lowers before I got the RDB BCG/Barrel combos. The Stern worked great as well, very reliable and bolt hold open also worked consistently, and I had no concerns about wearing out a piece of plastic or such.
Maybe the more recent Endomags are more robust in that aspect, but another thing to consider is that you can't do more than 30-rds with an Endgomag whereas there are a lot of extended-capacity options with Glock mag systems if that's needed...for like big stages of steel shooting or long PCC stages withtout the worry of reloading.