Be careful when loading your kayak after polishing it because the 303 will make it quite slippery to handle. I don't use it on the hull for that reason, only on the deck.
It is a UV protectant that doesn't leach out the plasticizers. Since it contains no silicones and is water based, not petroleum or alcohol based, it's a safer for the environment. But most of all, it works. It will protect your Royalex hull or the gel coat on your fiberglass or Kevlar hull.
Spray/Wipe it on and you can even just leave it to dry, though I use a sponge. It will protect your investment better than any other product I know of. BMW no longer recommends Armor All because it can leach the plasticizers. 303 won't. It can be a bit difficult to find, so try a local Marine store or order on line.