These are heavily planted, in my city, for shade, with no particular care given as to the variety, or whether it is fruitful. They are typically pollarded, sometimes, even twice a year.
I don't have any firm figures but believe that the wood has to be several years old, in order to be productive. If you prune, the new growth on a large tree will be useless, but little clones wills be fruitful, on account of their age.
I have seen all different kinds, except for the long, Pakistan one, which seems to be more expensive.
I have just learned of a pink one and will harvest some, tomorrow. There is a pink one, growing in a yard, then, within eyeshot, out of a crack in a parking lot. I can image where it came from, as they grow spontaneously, along fences, and my drip line.
I felt that the under-ripe black ones had a pleasant tartness to them, when still a little bit red-colored.. The older ones , which stain, were somewhat vegetable-tasting and bland. They were good in sour-flavored jello, baked with added sugar, and might benefit from some lemon juice.
I am curious as to what effect cross pollination may have, if from the fruitless male. They seem to have very long inflorescences, full of pollen. I have not created a successful graft.