This MP5 reloader works well with KCI curved 30 rd metal mags. It works well with most AC Unity 30 & 40 rd poly mags, which fit very tight additionally for some of the ACU mags, the loader claw would not snap down far enough to engage the mag due to the larger girth than KCI mags. I believe a little filing/sanding of the ACU mags will correct the issue. Quality/Workmanship is 8/10. Unknown long-term durability. Overall it saves my right thumb and I would buy again.