I've had them all. With a true scope I found that I had to keep my head up to keep an eye on the bird.
With open sights I find myself paying more attention to the beads/sights at times. I missed three last year because of it.
I switched from my SBE2 to my 870 that I had put an adjustable Blackhawk stock and red dot on. I found that I could aim and shoot with both eyes open as long as I kept my head down. I took the first bird that I had chance at and really liked being able to keep both eyes focused on the bird.
This year I have a Burris Speedbead/Fastfire for my Benelli that I'm going to try.