I have one, and they are complicated, but in semi mode, it really chews through ammo. They were banned from importing back in the '80's and hollywood seems to have bought many of them. They are getting tough to get, and pricey.
The SPAS-12 I have will not fire light duty ammo in semi mode. I ran a couple of boxes of 00 through it, and it chews that up real quick. I only shouldered for a few rounds in semi, prefered to shoot from the hip when in semi mode. Didn't need the abuse. Still a very neat collectors item, and can be fun to shoot, but complicated.