Thank you SO MUCH for posting this. I was waffling about whether to spend the extra for the Hera Arms stock and using ProMags to stay compliant and now I'm convinced that that is the right choice. Less expensive the M3 conversion may be, but I am not going to put inferior parts on my USC.I just got my kit installed and ready to go, and all I can say is I'm happy it was only $235.. Not pleased at all with quality, but also can't complain too much considering it's the only way I can use mags >10rds here, the mags are cheap (compared to UMP), and a UMP conversion is more than 5x the cost of the GG conversion, though you will quickly realize why. I had one of my buddies take all dimensions of every bit and piece in the kit, and what the dimensions were afterwards once he had to do some milling on the lower receiver and stock block and there are definitely some big differences. He also is considering getting into manufacturing gun parts because of how effed my kit was, and the quality he could offer similar options in.