That would work. I prefer a Mossberg 500 with a pistol grip (either one, your choice). First it is half the price of what you are looking at, secondly just jacking the round at the top of the stairs guarantees a urine puddle and broken exit window when you get to the bottom of the stairs. Thirdly, shooting down the stairs there will be no miss. You get no mulligan in this situation.
Having said that, you will find many that disagree with me. AND this requires a lot of practice for control. You shuda seen the old guy's face at Omalanden when I showed up wanting to practice with them years ago. He looked at me, then my daughter, then just shook his head and said, "C'mon, I'll take you."
A good idea is to start out with skeet rounds, then move up to bird shot. I use 01 in all of mine and the 3rd round is a slug. (you feel that one!)
Adrenalin is your friend when firing one of these in a case of necessity.
BTW, I hate shooting long shotguns so don't hunt with them. Anyone tells you they don't kick is a sadist.
EDIT: After he died, I took my dad's old Mossberg 500 hunting rifle and bought the 18.5" barrel and the pistol grip, both made by Mossberg, and made my first one. Just make sure the overall length is 26+ inches.
"The purpose of the pistol is to stop a fight that somebody else has started, almost always at very short range." -- Jeff Cooper