I used nothing but issue GI mags, with and without
the newer followers and NEVER had a mag related issue. Not in the Amazon basin, not in Astan, nor anywhere else I travelled and I burned up alot of unka sam's dimes in ammo.
Speaking of the mag detent failing I have had 3 separate PMags fail at the detent. All it takes is a small chip of that detent. Those were 308 mags. Currently replacing my pmags with SS ones. Maybe the 556 pmags are better.
That being said, $15 bucks a pop for a used mag I would avoid. Can you bargain down to 2-3/$15 maybe?