Silver wears really well, and if it does tarnish in time (we use TruSilver Deox, a type of silver that does not tarnish due to the alloy, so it shouldn't), it will still look great, since the keychain itself looks worn and tarnished.
It would not be shiny. Part of the process used to remove the Black Antique process requires satining, meaning the piece gets rubbed with a fine-grade sandpaper or a steel wool high-speed brush, so it would generate a matte, opaque finish, like when you see streaks on Steel.
You'd be more likely to wear out the jumpring and bail of the piece rather than damaging the piece or yourself. I will see about making strong jumprings and/or bails for it, but no promises there. You can always re-tighten the jump ring/bail should it ever fall out. Water should not be a problem.