it would be a rock solid excuse for missing or a handy tool for those that like sluice their birds on the water.
any time you shoot at a moving target and focus on anything but the target you will miss. the rib and barrel should supply a sight plane for your dominant eye to focus.
I could see how the dead ringer could help you keep your face down and eyes where they need to be, but if anything its just a bad aid for a poorly fitting shotgun and bad form while shooting.