birdman, what Jim said.. You really do not slide the stock, stock stays steady and the weapon actually slides.. Knob is to lock it so you can not bump fire it..
Well made, yes.. Fun at the range, get the feel of some rapid fire if you have never done it before..
Reliable? Takes a lot of practice to go through a full mag without stoppage, my experience..
Legality? 100% ATF approved..
Overall a fun novelty.. Would I want to land on the beach at Iwo Jima with one? Ah no..