AndrewZ, I have Kishu and its about 7yrs old. The fruits tastes very good, sweet with a little acid taste (tangy), just the way I like it.
It's a very good fruit to have, always seems to be seedless (0), and good fruit production. Keep your tree, fruits are very good, even though size is small.
Shaneatwell, I think your fruit may be bland because your tree is not old enough or if it is, then you should leave the fruits on the tree until the color is bright orange (they will get sweet). My fruits were just sweet for the first 3yrs, but now it tastes better to me since it has the same sweetness with a little bit of tartness as containerman mentions. I also have the Miyagawa and was not impressed with the taste of this big fruit (no taste, watery). If my fruits on the Miyagawa doesn't taste good this season I will cut off my grafts.
I picked some of my fruits this month for sample taste tests and since EricSC asked about the comparison taste test, I just did one today and here's my rating of the Kishu, Ponkan, and Kiyomi. Ponkan was the best of the three.
1. Ponkan - very good, with sweet/tart flavor
2. Kishu- very sweet, good ovreall taste
3. Kiyomi- good taste, lots of juice
I took a few photos when I did the taste comparison and will add a few photos later.