I've never used it on any of my boards and I've never got a ding or chip from a paddle wack.. Tape your blade.

IMO the best thing about rail tape is for resting your board on concrete for a rest while carrying it..

I guess you need to ask.. How fragile is your board and how often do you hit your rails?

Tape both and bash away with complete confidence. Over 12 months into a new board and it's still like brand new.
Not like it's going to take any performance away from a surf SUP.

This stuff is enough to do a couple of boards and paddles @ 30ft x 2" and it's proven to be as good as 3M leading edge tape in thickness and resilience for a margin of the price. I have a mate bring it over for me but there are companies you can use to onforward.
www.amazon.com/ISC-Helicopter-OG-HD-Surface-Guard-Tape/dp/B000QC6H90

I'm with you dj I reckon nitto tape the paddle
I hardly ever hit the sides anyway .
Thanks for the advice

Railsaver Pro tape!! It's the go.

18 months on my JP Aus, Exclusively used in surf and not a mark on them, great investment.