Opinion on them covers the entire spectrum. They seem to have a high warranty-return rate, but I gather that after the first (or second) return, they tend to be solid.
Never fired one. Handled a few at gun shows... I think the build quality is lacking. Since I'm pretty tall and have long arms, I found the short stock rather claustaphobic.
Upsides seem to be that there are models to fit multiple pistol manufacturer magazines (Glock, Beretta, S&W, Sig).
I have one in 9mm that takes Glock mags. Works great. Never had a problem with it.
My Grandson loves it.
I use it as a fun gun for general shooting, but it would be fine for home defense.
The sights adjustable (via the front sight), but are pretty basic.
I got one that uses Beretta mags cause I already had a FS 92 pistol. Never had problems with it. I shoot it as a fun gun, but keep it nearby for home defense if necessary too. 12 ga is my primary.
They are good and I got a 30 round mag with a 20 round back up in case the zombies or bad guys come in in great numbers.