I am interested growing Ugli tangelo because it is reputed to have monoembryonic seeds, which means that it can reliably cross with other citrus. The majority of cultivated citrus have polyembryonic seeds. This means that they have multiple embryos in each seed, and most of the embryos are apomictic, and thus will be clones of the mother plant, with no genetic contribution from the pollen donor.
In order to breed new citrus cultivar, it is most efficient to use monoembryonic types as the seed parent.
I have a young Ugli tangelo graft, on my Minneola tangelo tree, that made a single fruit this year. The fruit dropped in late Dec. before it was ripe, but the seeds look like they will be viable.
These seeds were most likely pollenized by the Minneola, since it produced the most flowers this year. But there is also a blood orange and a pomelo nearby, that could have contributed pollen.
I'm excited to see if any of these seeds eventually produce good (or at least interesting) fruit.