They seem to hold the mags as tightly if not more-so than the normal ones to be honest, I was a bit sceptical at first but am very happy with how they've turned out. I fitted them to my DCS, they have slight movement (millimetres but noticeable if you try to move it) if you try and twist them due to not having the molle weaved as many times but it's not a massive amount and are still very secure- especially when the final bit is folded back up under the elastic. When stacked next to another it's not even noticeable.
I've adjusted mine very tight and the grip the mags surprisingly well- haven't tried a stanag style yet, only pmags but I'll get round to it tomorrow, I see no reason for concern though, certainly a mag wont wobble out. I've only tried pmags as I say, but i'll try an m14 and whatever other mags I can find lying around to check adjust-ability too- though I'm very impressed so expect it again to be no issue.
Again I haven't skirmished them yet but from having a play with them I expect them to be great- the only thing I will say is that as I have them so tight, TM recoil mags can be a bit slower than normal aeg mags to put back into the pouches due to the cut-out for the bolt lock feature. The way I see it though is that I'm only ever going to be putting mags back in the pouches from my dump pouch when I'm sure it's safe and no chance of getting hit where I'd have a little extra time- it's only a second or so extra anyway but something to be aware of all the same.
If any of that didn't make sense then sorry, im tired lol.