The problem was NOT only with full-auto guns. Like the previous post, of the 30-odd magazines I had, 6 of them failed prior to green followers, none after. This is with semi-auto function. Of course, I had bought my surplus before the ban. There was probably a reason why they were surplussed! No problems now.
You only need the standard aluminum or old black plastic followers for the 20 rounders. The design of the 20 rounders does not necessitate the green followers. I'd get an extra-power magazine spring for them if you intend to shoot them competition. I've had a few failures prior to replacing the springs. Mostly with my new DCM upper and match loads.