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bmwstve , the BMS is built by mostly off the shelves component. And it need a sold separately USB cable and a laptop in order to change the boost gain setting.
RaceChip is weatherproof casing, higher speed CPU, and proprietary component. And you just need to open the casing for adjusting the boost gain via the dial.
Both tunes if you adjust the boost gain to high, you will get a CEL.
Also based in my experience and customers feedback, the RaceChip has smoother power delivery.
Don't get me wrong, I sell both of them.