Our yard is no stranger to the "un-useful" plant...plants that might have some usefulness but take an inordinate amount of work to make the fruits edible, not to mention palatable.I consider it excessive to grow a fruit that requires 5 pounds of sugar for every ounce of fruit.
Mind you, that doesn't stop me from doing it. First there were tiny, pink, fuzzy bananas, and now we have tiny, yellow, fuzzy oranges.
After 6-ish years of growth, one of our two flying dragon citrus trees (Poncirus trifoliata) has set fruit! From the small amount of information I can find on the internet, the fruit requires boiling before use, then you have to sort through the pulp to pick out the many seeds inside. Oh yeah, and it oozes some sort of latex-y substance that doesn't come off your hands even after washing several times. Sounds totally worthwhile, right?