I just re-did my nonskid with kiwi-grip this spring. I am very pleased with the way it came out. I'm really a novice when it comes to these things and I think that had I used some other options that are more difficult to work with I would not have gotten as good a result.
One good thing about Kiwi grip if you miss some spots or if the tape pulls up an edge or if your not happy with roughness of the surface you can re-apply and patch spots that you may have screwed up the first time through. I'm curious to see how well it will last but so far so good. I cringe when someone drops a winch handle or other hardware but so far it has held up pretty well. One other thing I noticed is that you should give it a least a week to really cure. You can walk on it after a day or two, but it really takes longer to really cure to a hard surface.
It does a good job of covering blemishes in the fiberglass of which I had a few my 1980 P-35.
My old non-skid was a basket weave molded into the deck. Because of this I had to use more kiwi grip than I projected based on their recommendations. I would say about 30 to 40% more.
Other helpful hints? Take off the painters tape within minutes of finishing each small section you work on. Good news is if you screw it up the first time you can go back over it and fix it. One other thing I did was use a 1" foam brush to create a flat surface for water run off along my toe rail and and under my hand rails. Not only is it functional to some degree, but I think it actually looks a nicer that way.
Would I use it again? Yes. Who would not be happy with it? If you're a real perfectionist and are willing fix any and all blemishes in your fiberglass and you are comfortable working with the more difficult to work with products you probably don't want to use Kiwi grip.