This Scottish invention has been widely used in the UK since the ban on peepers in the UK. It does not obstruct the chickens view, but prevents it from getting a good grip on another bird when pecking, and blocks the sharp tip of the beak from contact with other birds.
The birds will generally remove them in a couple of weeks, which has also been my experience with peepers. I suggest feeding crumbles or smaller pellets in wider opening feeders when these are used. I think the biddies prefer them to peepers, which can cause permanent vision problems.