I just got a DSA SA58 full length, standard barrel rifle and finally got to shoot it. All I have for magazines are the polymer mags, some of which I ordered and received well before I got the brand new rifle. When I went to shoot it, the mag catches (the little nub on the back of the mag) that the mag catch locks into started to wear out pretty fast just within a few uses at the range. The positive "click" sound they had when they were brand new went away and not only the click sound but the positive "feel" of being clicked into position quickly went south too. I found myself really pushing the mags upward and backward with force to make sure they were secured. Followed by pushing forward on the back/bottom of the mag to see if they would actually come out. No more positive engagement, just a vague "maybe it's locked in' maybe it's not" experience.
Once one of them came loose a touch enough during fire that the next round did not get picked up by the bolt. I think it was a second or third shot. And so when I went to shoot, all I got was a dry snap and of course safety being first, I waited for a full minute to eject the round in case it was a dud. But of course there was nothing in the chamber! The round didn't chamber because the mag was slightly too low. As a former L1A1 user back in the day (I had real metal surplus L1A1 mags) I was not impressed.