The bead is fine for most uses.
If you want to see what a bead sighted shotgun is capable of, google "Hickock45 Mossberg 590". He easily and repeatedly hits his 80yd gong, as well as other demonstrations of accuracy.
I have fired pretty tight 50yd groups using slugs in my bead sighted Mossberg 500.
The best reason to have sights, I think, is the Federal Flitecontrol buckshot...it shoots so tightly that sights might be pretty useful.
Still waiting for my Flashback...I would like it now, please.