Easy setup and very reliable - Mean Arms 9mm Ejectored EndoMag - 3 Pack

Super easy to install into mag shells and revert if necessary. With my FM9 upper on a Ruger AR556 lower, they required no break-in as there was already plenty of clearance. After a few hundred rounds, I have had no issues whatsoever. The plastic ejector doesn't seem to be worn at all yet, but I can see this as being the weakest point over time. One downside has been mentioned many times by others, but you do have to have the mag inserted to clear a chambered round. Not really a deal breaker for me.