I have some ugli fruit seedlings I grew from a fruit I found at a supermarket I'd be happy to give away, but it probably wouldn't be worth all the trouble I'd have to go through since you're in Europe, getting a plant certificate, and whether it would even survive the delay through customs. The taste is kind of like a watery kind of bland navel orange, with just a little bit of grapefruit.
Anyway, the ugli fruit I tried didn't really taste all that good, although there is something kind of unique and spicy about the fragrance in the peel. The flavor is like a kind of watery bland navel orange with maybe just a little bit of grapefruit. It is very juicy though.
You're not really missing anything, and anyway I read ugli fruit doesn't deal well with the slightest bit of cold, so it may not be the most appropriate choice where you are.