Much of debate over peep sights and or ghost ring sights. Let me just say this, when confronting a threat or searching for a threat you are really amped up and your eyes are bulged out looking down range. With a bead or rifled sights the sight is forward and in your peripheral vision and easier to pick up when the threat is confronted. High speed operators in the military and Law Enforcement now place their red dot sights forward as far as it will go entry carbines so they have a wider field of vision and the sights are easier to pick up when you need them.
Another factor is proper use of GSR type sights. You need a good cheek weld and your nose as close to the sight as possible. Some find this harder to achieve or maintain with the recoil of shotguns. I can use a GRS just fine on a combat shotgun but for room clearing a bead front sight or rifled sights. With a GRS on the receiver it is much harder to use front sight only shooting (reflex, point shooting...,) as they teach for close range work at Quantico.
You want a GRS go for it. Nothing wrong with it just practice allot and prepare yourself. If you have the occasion to do scenario based shooting or force on force like simmunitions you will appreciate a bead or rifled sights in a typical house structure. Better yet have someone set up shoot / no shoot targets for you with corners and blind spots within five to seven yards and then run the exercise with ghost ring sights and a bead sight and check your times.