My view FWIW is would you wear a screen protector on a 'normal' watch? I know I don't. And before anyone says about the value, I have a couple of higher value watches as well as old 'sport style' watches.
A phone I think is a different thing, it is in the hand, pocket, bag etc and can be dropped easily. A watch may get knocked, but all watches do.
I have a S0 SS and a S2 SS, work out with both, do the gardening etc and the screens are perfect still. Every few months I buff up the stainless steel with a cap cod cloth or 'mothers' cream and they both look like new
I think just enjoy the watch and don't try to cover it up