Had a boat owner buy one for boat defense purposes. He's been using it on his boat for about two years now with no reliability issues. If it can survive that abuse, I'd have no worries about using one. Any semi or pump can jam. The pump is not sensitive to weak, target type ammo. The Siaga should be fired with your preferred load ot be sure it works. That load will probably be full power buckshot for optimum reliabilty. You can fire the pump with anything that will fit in it. The Saiga can fire them only as an awkward single shot.
It's a lot clunkier than any 870 or 500, though. so if it's "better" depends on how important a compact design is to you.