I have a Benelli M121 M1. It's a good reliable shotgun. The only thing wrong is there is a design flaw that was later corrected in the M1 Super 90. There is a button on the right side of the receiver that you have to depress to get the shell lifter to raise when you load. This makes loading with the support hand while keeping the weapon on target a tad difficult. It can be done, but it's not as smooth as with the Super 90 or a Remington or Mossberg. Supposedly at one time there was a modification made to fix this problem, but the kit is pretty much unavailable now.
You have to hold it tight against your shoulder for it to function. If it doesn't have a solid surface to recoil against it will malfunction. Of course that's not really a problem, you need to provide a solid platform to shoot any shotgun well.
I like mine. If you can get into it for a good price go for it. They are good guns. I used mine in Louis Awerbuck's Stage 1 Shotgun course back in 2003. It held up well. It was a pain fumbling with that button though.
Jeff