For defense shotguns when using slugs or buckshot they are excellent ! Fast and accurate ! They are excellent for rifles for hunting too, accurate enough to put them in 1" groups !
. I prefer a 1/8" square front post and a 3/16" hole in the ghost ring rear.The concept is that the eye automatically centers the ring to the eye so you only deal with the post.The ring then must be mounted close to the eye.