I purchased one of these toys and it is indeed nifty.
As a side note S&W is now selling spare mags for 20.04 a piece:
Product: M&P15-.22 25 RD Magazine
The only "downside" to this rifle is the rather unsatisfying bang when you shoot. The first time I shot the rifle it was like:
Wow this is just like . . . the stapler
Seriously shooting the 15-22 had all the recoil of the stapler I used on my target stand.