stu8v, As edde said we have worked closely with fastchip on this one to be able to map the original i.e. the system has been cracked.
To put it simply, we can of course map it to do almost anything that a whole aftermarket system would do and certainly a hell of a lot more than a piggy back item. Also it is very stable, by this im not sure how well piggy backs will stand up to confusing the original item long term, which could lead to possible shut down. I know a certain person who had this trouble when trying to use a piggy back for a turbo application.
Doing it this way retains any of the features and items of which the ECU speak to unlike full aftermarket kits which feature new looms and sensors. We are currently working on throttle body kit which will retain the most of the standard sensors, but will be ultimately be controlled by an original re-programmed ECU.
We will offer custom re-maps on a minimum of 10 cars at roughly £350 + VAT, which is a very good price for what you get.