I suppose I ahould clarify.
Will a bead work? You bet. Will a set of Rifle Sights, Ghost Rings, or an optic of some sort work better? Of course it will.
The shotgun is a contact to 100+ yard weapon. For it to be effective in all arenas, it needs more than a simple bead for optimization.
I will cede that I am coming at this froma bit of a different perspective, as a Law Enforcement officer. The shotgun is the do all. It must be able engage at all reasonable distance, and do so accurately. By default, my work shotty is my HD shotty as well. I have the utmost faith in my 870, whether it be for critter in the back yard, to bad guy in my daughters bedroom, to the freak 125 yds down the street popping at me with his 30-30.
I have gotten to the point that my duty loadout is 100% 1oz slugs. Six in the tube, and six on the sidesaddle. I carry a couple boxes buck in my duty bag, but they are extras. If a 1oz chunk of lead wont do it, then nothing will.
While I love my AR, there is no more versatile weapon than the 18" bbl 12 gauge shotgun. Limiting the gun with a bead sight fails to recognize its true abilities. If thats fine with you, great. I fail to accept anything less than what it is capable of.