I recently built a 9mm pistol ar upper and rather than build a dedicated pistol lower for Glock or Colt mags I thought I would give these a try and utilize my 300blk pistol lower. The concept is great allowing you to use a gen 2 or 3 30rd pmag and just drop the endomag guts in for the conversion. From the beginning these things kind of scream cheese and during manually cycling of dummy rounds I was not impressed. The ejector and opposite rail lock that snap over lips of p mag are rather flimsy and easy to bend. I did not have high hopes but reserved judgement until I did live fire test. Well this weekend I did just that, firing my 9mm upper for the first time. I have to say despite the cheesy appearance, I did not have a single malf through 120 rds with two different converted mags. The plastic ejector built into the mag adapter means that if you want to drop a mag with rds remaining and then clear chamber, you have to reach in action after locking it back and removing live round from bolt face with a tool or a finger unless you got sausages like me. The other thing that is not quite great is the fact that you must seat loaded mag with action locked back as it wont seat in otherwise and they do not recommend trying it. Other than these caveats the things just sorta worked feeding and ejecting great. The action also locked back on last round every time. I used 124gr blazer brass ammo and Wolf 115gr military classic steel ammo and both ran fine. I also shot a mag of each supressed with no issue other than on a short coupled pistol build, the smoke that permeates the action kind of gets to you a bit. I am not sure how the longevity on these will be but I will give them a fair shake and give another report after some extended use. They are a bit spendy at $28 a mag or 3 for $80 or so. Of course this is on top of the cost of the 30rd pmags. It is a neat concept and I hope they stick around long enough to improve upon this design.