Great value - Pro Mag AR-15 / M16 9MM Magazine Adapter Block For Colt 9mm SMG Magazines, Quick Change

for the money I could complain, have only used the promag reinforced polymer magazines but has been pretty solid. since purchase have run 1000rds with no malfunctions. my only criticism is the seating of the magazines that occasionally will over insert with the magazine open. I will experiment with other magazines to see if related to the polymer mags but so far has been a great experience.