Have been looking on the internet at these tuning boxes that you plug in and some of them give up to 30% power increase. That sounds quite nice but also they claim to gain around 5-7 mpg which is rather good aswell. Has anyone got one of these on a Mk3 or another DCI? just wondering if it's worth it and also if any damage is done to the engine with one fitted. I heard that engine runs a lot smoother with one fitted but have heard the revs are increased slightly. Does that mean the engine will idle higher than usual? any info would be great. Thanks!