6 star and muscletech are both owned by iovate. I would suspect identical product in different packaging.
Different products somewhat, but yes, they are both owned by Iovate. BPI is not, their headquarters is in Ft. Lauderdale, Florida, which I just may visit on Thursday, along with BSN/Optimum before the NPC Nationals.
Six Star is mainly a mainstream line in various FDM (Food Drug Mass type of stores), whereas Muscletech is a more hardcore line. The products are a little different though.