They are, and would be. Rimfires are [currently] exempt from AW laws, so it wouldn't do much from a legal standpoint in this state in regards to the M&P 15-22. Now, if you made one for what would be considered an AW (centerfire, semi-automatic rifles capable of accepting a detachable magazine with any "evil" features), you'd be onto something. However, I see the description says the slots are not open (essentially making it a larger thread protector) and the small pictures underneath show it as such. However, when I look at the larger photos about 1/3 of the way down the page, it shows the slots to be open? If the slots are indeed closed and looked like this...:

...it should be an acceptable solution for those wishing to do a "featureless" build on centerfire rifles. It would/should be considered a thread protector. Right now for such builds, you either use a thread protector (making it look like an M&P 15-22 without a threaded barrel), a brake/comp or an un-threaded barrel.

IANAL; that's just my take on it.