I saw one back around 1990 in a pawnshop in Utah. It was a polymer brown junky looking thing. One piece went in front of the magazine well and one behind, allowing regular AK mags to fit between. The AK mag included with it were also a juky polymer.
I thought it looked like a peice of junk and didn't get it, determined to wait for the good quality metal version. My dumb mistake - bans, legislation, gun scares, and whatever conspired to the point this never happened. I've never seen another version of it or one like it since. I don't even know who made it or what it was called........
Wish I did buy it just to know how it worked. Even if it was a real POS, I have some buddys who would spend good time trying to reproduce it and make it work right.
Oh, well - hindsight is 20/20!