Denise I faced the same choice this month. Whiskeyjack is getting a makeover, and new non-skid was on the list. I considered Kiwigrip and rejected it in favour of Interlux intergrip non-skidd additive, after talking to a kiwigrip rep, the local yard, and reading some of the info here. Here's why:
1. Colour match. Couldn't guarantee it would match the rest of the new deck and cockpit paint, and nobody could tell me whether it would fade the same. by adding intergrip to the Paint i am already using for the rest of the deck, no problem.
2. Uniformity of finish. IF you are doing it all yourself, and IF you aren't wroking on a hot day, and IF your boat is not in both shade and sun depending upon time of day (meaning some parts of the deck will be warmer than others, causing paint to lay differently) then you can problably get a nice looking uniform finish. But, I am working with my wife, two people, two trays, two rollers, two techniques- the kiwigrip is a very thick material that doesn't really "flow out" very much, a lot like a roll-on truckbed coating, and is sensitive to technique- it stays as it lays, and if you worry it too much, it gets peaky, like meringue. Intergrip can be rerolled and recoated prior to getting tacky (15-30 mintue working window depending upon weather) to even out imperfections, but if you try to recoat Kiwigrip it can get messy. Also, painting on a hot day will cause the roller to load up and clump up, leading to an uneven coating, unless you give it a periodic cleaning.
3. Cost. A half pint of Intergrip is $15 at the local scamdlery, enough to do the entire deck of our boat (added to a quart of Brightsides.) According to Kiwigrip, I need a GALLON of Kiwigrip to do the same area- $130, or thereabouts.
4. Appearance. I like the way intergrip looks. Here's how ours looked after we finished this morning.
The Kiwigrip may be a little grippier if properly applied , and may last longer, if properly applied, but since I and my crew occasionally have trouble with "if properly applied," I liked the idea of getting decent results with a more forgiving material.