I have used water shed.
It seems to work reasonably well.
Doesn't make feathers stiff.
Doesn't really make em water proof either.
It does keep a very substantial amount of water beaded up though.
I have never used it on fletch tape.
However when you put it on I see no reason why you'd have to get any on the fletch tape.
It comes in a bottle similar to a visine bottle..just smaller.
The thin fluid comes out very controllably ( can do a drop at a time easily )and wicks up the feathers nicely.