There is a bid difference is MMC rotors. It is all in how they are made. Ray Wheeler AKA w8less (Screen Name Turbo ray 44) sold rotors that exploded. This was not because of the actual metal they were cast with but the method they were made by. Ray does not sell these same MMC's any longer but these rotors are still made and sold. Buyer beware, read and do your own research before purchasing.