Does anyone have an opinion on the tiwanica?
I've never personally tasted it before, but from what I've read it's not really eating quality. The Japanese used it to flavor vinegar, and as an ornamental, including using the branches full of fruit as ornamental decoration. It's a very vigorous grower and, as the Japanese name daidai implies, the fruit hang on the tree for a very long time.
I would imagine the fruit quality is much like a somewhat lower quality sour orange. If that's the case it may be useful for certain culinary uses, like perhaps making a marmalade, but is not something you're going to want to eat fresh out of hand.
I think one of our other forum members can comment on how they taste though:
The Daidai citrus I've had at past citrus shows were nasty bitter orange. I wouldn't eat it but that's just me.
(Taiwanica sometimes goes under the name Nanshodaidai or daidai)
Laaz, Charleston, SC 9a , said they tasted like "nasty bitter orange", "I wouldn't eat it but that's just me"
I don't know if this helps anyone at all but I've tasted Chinotto sour orange and can relate to his sentiments. The sour orange is theoretically edible but just very sour, not really the best flavor, despite the nice intense aroma, and perhaps a little bitter, though nothing like the type of awful bitterness from poncirus and its hybrids.
I could snack on one of the fruits while foraging if there was nothing else better to pick, though it's pretty seedy, would be more for the adventurous eater.