According to Magpul reps, the 5/10/15 Pmags are based on the 20 round Pmag bodies with new locking plates, which limit the follower from going beyond the prescribed limit. They are intended for states with hunting capacity restrictions or agencies who wish to have magazine limits under 20 rounds. They didn't have pictures of these plates, but it's the plate between the spring and floorplate.
I'm not sure how our laws would deal with these magazines, but it doesn't seem to be a permanent modification to the magazines, although they are designed to limit magazine capacity.
US MSRP $13.95 and release date of summer 2010.
