I also do not know much about Ninja Mites, either.
From hunting around the board, I think I have determined that the main distinguishing characteristic between Ninja Mites and series 2 Exogini is that the U.S toys have white paint appliques, whereas all Exogini do not have this. Is that correct? Are there other ways to differentiate between the two toylines?
Such information will help me in sorting out the identities of the very small handful I have of what appears to be a mix of both S2 Exogini and NMs.