Here's my take on "legality" and usage:
If the ATF says the thing is legal to make....
and legal to own....
and only 'becomes' illegal when you use it in ways not intended by design, such as placing against your shoulder.......
then I submit: who's monitoring said usage to make sure of compliance?
I mean, if you are practicing home defense scenarios at the range or doing dry-fire drills at home, who's watching to bust you for it?
Now if you use the thing in a high profile way, such as a "caught on tape" situation, then it's just one more charge for the DA to levy against you.
But in a SHTF scenario, that's the least of your worries, I reckon.