When it comes to 5.56mm HK roller-lock rifles and their clones, three choices are prominent in magazine selection. Choice one is a version taking inexpensive and widely available AR15 magazines.
Choice two is the original German steel magazine, currently at $80 ea. They work great and would be my top choice for serious use.
Choice three, a bit unexpected, is the Promag polymer 30-rounder at $14.95. I had a chance to try it and was pleasantly surprised.
It locks into the mag well with no wobbling, feeds reliably and generally behaves like a quality magazine. I have not done destructive testing on it, but it should at least survive being dropped at the range, in part thanks to much lighter weight. At 150 grams vs. 270 grams for the HK original, it gives five loaded Promags for the weight of four HKs.