Problem is even if use of a NFA is justifiable as self defense, your NFA will be seized as evidence pending that determination. In the city where I work, the cops assigned to the property room are all selected because of their disinterest in firearms. They'll stuff that $10,000 rifle down the 55 gallon drum along with the $15,000 Perrazi and the $100 H&R. It's just a gun to them.
That's why for my personal self defense I'll use the cheapest gun which is reliable.