I was looking through the NAA forums, and Pietro posted a link to this post on Rimfire Central. I've sent a private message to user Teddy Bear Rat in order to get to the bottom of what this modified NAA Mini Revolver is all about.
My initial thoughts are that it would be fun to have a little mini revolver with a long barrel and folding stock. At only a little over a pound, this is one rifle that won't weight you down! He was shooting Super Colibri, which is 22 long rifle. I'd like one in .22 Winchester Magnum. That would be a fun gun for sure. There are obviously ATF ramifications, and they are described in some detail in the postings, but I would like to know much more. I'll let you know if I find out.