Peepers do work to stop the behavior and in many cases, the behavior won't resume after removal.....
However. There are hard cases where the feather picking and bullying seem to be hard wired into the brain, and I've had chickens resume their bad behavior while wearing the peepers.
If you're interested in various methods of trying to control this awful behavior, here is a gonzo thread covering my and other people's attempts to deal with this issue. Believe me, it's very complex.
https://www.backyardchickens.com/threads/i-think-i-found-a-miracle-cure-for-feather-picking.697052/