I have the MWG 75 rounder, plastic, and it seemed to work well enough in full auto, but I only used it once or twice. I did not like how it stuck out to the side, was bulky, and made the rifle very off balance. I got the Beta C mag, but except for pictures, I haven't actually used it. I have a problem with abusing my gas tube. I have heard bad reports about the Beta C, but from what I understand, they were not built for endurance but were supposed to be more of a one time then throw away deal.
Once the AWB sunsets, perhaps the Beta mags will drop back down in price to something reasonable. They should not have to cost the price of an entire stinking rifle. I will also be wanting a Beta C for my MP5, FAL, and others I am sure will want the HK91/93 units. What I really want are some .22 rimfire drum mags! YEAH!!!!