Older post, but after just trying a couple different ceramic coatings, I wouldn't use them on any handle scale ever. They are also slippery, especially when wet or damp. Not a good thing on a knife handle.
Hmm.... maybe the blade of a knife, sword, machete, or axe when it doesn't need to be food safe though. Or the metal fittings on sheaths or scabbards. The DIY spray on, and the ones used by most dealers requires getting it wet, spraying it, then rinsing it so might not be the easiest thing to do on a wood or leather sheath or scabbard.