PMags are what I use. They work much better than USGI metal mags when loaded and stored with 30 rounds, are very rugged and reliable, and can be had for under $10.
I haven’t seen metal feed lips to be an improvement or a detriment over the polymer feed lips of the PMAG, except when it comes to being dropped. The polymer feed lips of the PMag will flex and not crack. I’ve seen metal AR mags, and polymer AR mags with metal feed lips, take damage when dropped on a hard surface and landing on the feed lips. The feed lips can become bent and won’t feed properly.
I haven’t seen metal feed lips to be an improvement or a detriment over the polymer feed lips of the PMAG, except when it comes to being dropped. The polymer feed lips of the PMag will flex and not crack. I’ve seen metal AR mags, and polymer AR mags with metal feed lips, take damage when dropped on a hard surface and landing on the feed lips. The feed lips can become bent and won’t feed properly.