If you like to follow meticulous instructions (in Japanese) and have some complicated fun with your food, then this is perfect treat project for you. It's also good if you don't really care that much about how your food feels in your mouth, or how it tastes. As far as being an activity to waste about twenty minutes of your day, this is a great candy. This is not something that you can just finish up in a few minutes and eat right away. Even when you understand the instructions, it takes a lot of patience to get your hand made fake candy to look even close to acceptable.
As far as being a candy on its own, it's not great. It looks really cool, and it makes you wonder how several packages of powder could possibly turn into something so interesting, but it's not objectively a good candy. The rice has a really fruity flavour and the texture of marshmallow, the sushi is kind of slimy, and the seaweed is really chewy. The only part that I really loved was the fish eggs. They were cool to make, they kind of had the texture of real fish eggs, and they tasted really fun too (and nothing like fish). I had a few fish eggs left over after making my sushi and I ate them all up.
If you get your hands on one of these sushi kits and you're curious, go for it. Leave lots of time to make it, and try not to think too hard about why these chemical reactions work (or more importantly why you're going to eat so many strange chemicals). We had a fun time putting these little rolls of sushi together and while they weren't that amazing to eat, it was a nice little reward after all the work.