Works very well (if you install it correctly) - Stern Defense MAG-AD9 AR-15 Glock 9mm/.40 Magazine Conversion Adapter

I installed the Stern Defense MAG-AD9 in an 80% lower that I finished and it works very well. I suspect a lot of the negative feedback is due to improper installation. Sure, follow the instructions, but you have to understand how the adapter, especially the LRBHO mechanism works. Remove the upper during initial installation. This way it is easy to see how an inserted mag interacts with the adapter. Insert the adapter as described. Very lightly tighten the center hex nut that fixes the adpater in place. Then, with a mag inserted pull downward while keeping the adapter parallel with the magwell front to back and left to right. Keep an eye on the LRBHO arm. Make sure the arm is sitting over the correct spot on the mag follower. Do the final tightening when this all looks correct. The LRBHO arm is thin and can bend if pushed too hard, so you may have to push it over the correct spot on the follower. These days it's hard to find a dedicated 9mm AR lower and if you do it will be expensive, AND, it will not have a compatible LRBHO mechanism.