I've used neverwet on an e-z up 12x12. I would say that the square footage of this canopy would be similar to 8/9m kite?! Anyway. I needed 2 cans to cover the canopy. It dries up a bit hazy/milky, definitively not clear, and it feels a bit sticky. Yes, water pearls off nicely, but exposure to UV destroys its magic fast; I would say within 14 days.
So, overall, would I use it on a kite? Naw. I think one would need 2 to 3 cans to cover it, befriend the haze and do it all over after a month for ~$60.
I agree, water launch is a bitch. So, curse at your kite. It gets afraid and may turn over easier ...
peace