Got it last week. Installed it on the lower but haven't had a chance to fire it yet because the upper is at the gunsmith. It seems to be rock solid, the only issue is that it seems the mag doesn't click into place when you first push it into the mag well and pushing it harder gets the mag too far up the magwell, which it warns against, however when you back out the mag a little then the mag clicks into place. i will have to try it with the upper installed to verify if this is a real issue or not.