I like a mid-bead as a training aid. Especially on a newer shotgun. It helps me satisfy myself that the shotgun is mounted properly and that it will shoot where I am looking. I don't use it as a sighting device or aid. I just look at the target over the barrel and shoot. Seems to work for me.
A "training aid" is a good description of how I sometimes use one. I don't shoot a lot of clays, and it's not unusual for me to go months without using a particular shotgun. If I haven't used one in a while, the mid-bead helps as I practice my mount. It's not a big deal, but I do use it in that way. Duck hunting in cold weather when wearing a lot more clothes than what I've practiced in is another time I like to practice the mount and the mid-bead can help.I don't notice it at all shooting a moving target.
Maybe I am the only redneck on this site, but a shotgun is sometimes used to shoot stationary game, and that requires aiming it like a rifle. I have definitely used the mid-bead in shooting turkeys, squirrels, and rabbits over my life. Those of you who only shoot in tweed jackets may not even be able to imagine that such people as me even exist, but the shotgun manufacturers did and were willing to put the mid-bead on to help us feed our starving families.
Ok, as Foghorn Leghorn would say, that's a joke, son! You should laugh when you hear a funny joke.
The days of me using a shotgun and a mid-bead to feed the family are mostly over, but that time really did exist.
