I have seen these sort os of mags in the past, Mostly on 10/22 hi cap and barrel types of mags, But the Best I saw oither wise was for th Syer AUG, it was a 30 or 40 rnd 223 magazine and I saw them do the drop test and the test where there showed how tough it was and it didn't ever fail? These were about $45 and that was like 7-10 years ago< I did see one place that had 30's for the AK, but they dropped off the net? Hope this hlpsm some small degree?
If the mags are for an AK and are U.S. made, you may want to be wary of them. For whatever reason, most U.S. made AK mags just do not work as well as the Russian, Chinese, and Eastern European mags. Many AK owners will not even buy U.S. made mags.