I would like to see a reference to this claim, as far as I know, Matrixport was founded by Jihan Wu. Jihan Wu is not Bitmain, it just so happened that the former is the CEO of the latter, I also know that Bitmain as a company might have some shares in Matrixport, but that does not make Matrixport Bitmain's exchange.

With that being said, I wouldn't touch an exchange that has anything to do with Bitmain or any of their current, former or future CEO with a barge pole.