Yes, as far as color matching, what I repaired was the keel, and therefore I wasn't going over the color match with a strict eye. Its a little off color, but not by much. If it was going to be in an area that is noticable above the water, I would spend the bucks to have it professionally done. I was quoted a few hundred dollars for the keel repair when this stuff cost me 40-some dollars and a few hours while drinking beer.
As far as sanding, the little strip of sand paper that comes with it is very fine grade. I would get a couple larger grain strips of sand paper to sand off big excess chunks, and then use the fine stuff to smooth it out. Thats what I did and sanding wasn't that hard, but I can see how it would be if you only used the little paper that comes with it.
IMO, if all of your dings are below the rub rail near the waterline or beneath it, I would buy one of these kits, test it out on a good sized ding on the bottom where nobody will notice if you screw it up, and see how you like it. Like I said its pretty cheap and the alternative may be very expensive, especially when talking about a PWC which all get scuffed up on the bottom with time.