It's more of a personal issue, IMO. Excellent shooting can be done without a bead, obviously. I still prefer two beads on my comp guns, not because I need them to aim, but because part of my pre-shot routine involves looking AT both beads immediately after premounting to confirm a perfect mount. It's just a personal quirk in my routine, that I do before every shot. And, it works for me by instilling confidence that the "the world is right" just before I say "Pull!".
Once I confirm the perfect alignment of the beads laterally, and see them sitting "on top of each other", I never notice them again consciously. I'm totally focused on the bird.
My hunting guns are not mounted until the second before the shot, so it's entirely different with them.