I tend to agree with this, though the Remington 870 has proven to be old reliable. Also, having a shorter 18" or 18.5" barrel is important when swinging between doorways and hallways. Any shorter, and you lose mag capacity. You may want 4-5 rounds at your disposal without reloading, so no double barrels.
In WI, no waiting period for shotguns, but there is the damn government paperwork.
Have you gone to a local gun show or estate auction yet ? You may find a private seller, no paperwork on file required. Find any 12 gauge, semi-auto or pump, and just saw off the 28" or 30" barrel to get your 18".
There's another whole argument on ammo: 00 Buckshot or a traditional hunting round ? When it comes down to it, even #7 from a shotgun will do enough damage to stop them. 00 means many rooms of drywall repair. Which means less chance of a lawsuit.
I hunt so I'm looking right now at Mossbergs with a set of interchangeable barrels.