Does anyone know if "Flying Dragon" is a variety of Poncirus trifoliata or is
it a variety of something else?
As others have noted - yes it is Poncirus trifoliata. It grows in a
twisted/distorted manor, which provides dwarfing when used as rootstock.
How bitter/ tart are the fruits? Can you make anything half pleasant out of
the fruits? Marmalade?
I am not sure, but Edible Landscaping used to sell complex hybrids of
Poncirus and Citrus, that were [supposedly] less cold hardy, but more edible.