Last week I posted a "range report" of my experience using bead sight, ghost ring sight, and red-dot sight all in one "let's do a comparison" day at the range under tactical competitive conditions. To save you the trouble of searching for it, my bottom line on adding a red-dot sight to my Mossberg 500 is two-fold:
First, I liked the red-dot but it offered little improvement over my bead results under 50 yards. At 50 to 100 yards, my tired old eyes really loved the red-dot sight picture, and I shot just a little bit better than i did with a bead (YMMV... the instructor said I shoot really well with a bead among a sea of ghost ring shooters). With practice my short-range snap shots with the red-dot might get as fast as I do with a bead.
Second, you'd need to figure out which mounting system you want with the red dot... anything that does not allow you to instantly use the bead (e.g., a see-through or see-under mount) is a disaster waiting for a battery failure to happen.
I'm now trying to figure out why, for my shotgun usage scenarios, I'd want to spend money on a ghost ring sight, even tho I really liked my results with it.
--Bruce.