I agree that the shave ice at the resort is very good, had it our first trip. This second trip we just had, we did try Matsumoto's on the north shore. Loved the ice cream on the bottom, but did not care for the beans at all (they were like kidney beans). We opted for the extra 30 cents for the plastic thingie to catch the drips, as we were walking nearly a mile to get back to where we had parked the car for our Giovanni's shrimp truck fix. The line at Matsumoto's was long....about 15 minutes. I can't really say if the shave ice itself was better or not. There are alot of fun shops and places to eat in that area (aside from the shrimp truck)
If you are going to be up that way, I would recommend doing both! Lunch and dessert. The garlic shrimp is amazing. Giovanni's can be hard to find...make sure to go to the correct truck, there are a few parked in this gulley area.
http://matsumotoshaveice.com/
http://giovannisshrimptruck.com/
Have fun.