I have the Bluefin User Guide in front of me and it states:
"With our established reputation as world leaders in engine management system tuning we are convinced you will be happy with your Superchip. So much so that we offer- refund* within seven days if not completely satisified
- lifetime guarantee
- Superchip Warranty
*This is our seven day 'customer service guarantee'. Your statutory rights are not affected." So it would appear that you have a 'try it and see' option. According to the Superchips website, you'll get a modest <10% increase in power and torque http://www.superchips.co.uk/curves/minicooper.pdf