Machineguns are not the only NFA item suitable for defense.
I realize that - must not have read the rest of my post......
Now, if we are talking suppressors - I guess you could always use it, take it off when your're done and toss it back in the safe or whatever. That wouldn't be too hard. Enough said on that.
As far as SBR's - if it wasn't for the difficulty of storing it when not in use, I'd say that would be a pretty good choice for inside your house. Large capacity, more accurate and more powerful than a handgun and easy to use.
Sorry I didn't mention sawed-off shotguns, but IMHO, it's basically the same as an SBR.