"I had a Rock Island Armory M5 12 Gauge and it was garbage. You get what you pay for really. I bought it brand new and had trouble with it from the first time I took it out. About every 4th or 5th shot it wouldn't fire. I would have to rack out the shell because it thought it fired but it wasn't. I took it to a gunsmith after a friend of mine couldn't figure out the problem with it and the gunsmith was as clueless to the cause as I was. When testing it they had the same firing errors I did. His advice was to get a new gun and avoid Rock Island products in the future, which I have. I wouldn't take a new Rock Island 12 Gauge for free at this point. A lot a good a gun does for home defense if you aren't sure if it will actually fire or not when you pull the trigger."
If you want a cheap reliable shotgun for home defense find an old Sears JC Higgins Model 20 and hacksaw the Dial-A-Duck choke/porting off the barrel. That was my first defense shotgun and it was built like a tank. High Standard actually made them.
Or for new just get a Mossberg 500 or 590, followed by an 870. My pure defense shotgun is a 590, and has been for the last three decades. It's been used hard and has never had a failure. Totally reliable.