I went with the PTG one and it works quite well. As hunter said, if you want to use standard AICS mags then go with CDI and get your stock inletted. I think the no mod is for the newer B&C stocks that they use on the stealth model. I had one of the older stealths in a HS Precision stock and even the PTG requiring some inlet work that I did myself.
The AI AE mags that he mentioned are a slightly skinnier body than typical AICS mags. If you have any questions feel free to PM me.