I have trouble with most devices despite loving the fetish, but I heard some cherrykeeper devices are good for growers. I am 2.5 inches flacid and 7.75 inches hard, can I get a cherry keeper that will be comfortable?
They are very good devices, but no better or worse for the question you ask. Generally accepted is that a cage length close to your flaccid length is best.
A caged erection get's painful if the cage is not large enough to allow you to grow to your full size. Once you get started, you will push the cage along the growing shaft, pulling the testicles along with it. It might start to feel like your cage is trying to pull them right off. So that leaves you with a few options I suppose 1) size your cage to allow a full erection (This might be hard to hide under your pants) 2) size your cage to your flaccid length so erections cannot get started. (seems to be the generally accepted practice) 3) embrace your inner masochist (have fun, I guess)