To add to OOL's reply, I find anything more than a little brass bead on the muzzle to be a distraction. I informally "self-train". One of my sessions is to practice not getting tunnel vision with the gun at full shoulder mount.
Walking around in both lit and darkened rooms with the gun mounted and using my eye travel to cover various directions while keeping my gun pointed at a fixed object.
With rifle sights, both the notched rear or peep/ghost ring, I find it more difficult to maintain distant focus as my eyes sweep past the sights. They catch my attention every pass.
The bead can be removed and I wouldn't notice it until I was "aiming" at a feral cat or squirrel as I gauge distance and thusly the height my muzzle must be in relationship to the target to get a one shot kill. I understand there are a ton of cat lovers and I try not to disrespect them by having a gun shot feral cat dieing on their lawns.