Hah, BMW tax eh?
I think the price being higher than the other Standbacks has more to do with the development effort than it does any arbitrary BMW tax. cp-e has been working on this controller for as long as I can remember, and they've devoted a considerable amount of resources into bringing a configurable engine management system to this market. So in a way I'm not surprised to see them charging slightly more for the BMW application.
Although it does cost more than other systems on the market it does have some unique features that others have yet to offer. I think you guys will be pleased with what you're getting for the money.