from what i have read it varies mate, depending on how well your car is earthed at that factory
i was always very sceptical and was def NOT going to buy one !!
then i saw one 2nd hand at a good price it def worked for me, much much smoother when moving slowly and on tickover and better mpg
all it does is increase the earthing/grounding on the car which then in turn allows for cleaner signals from the components to the ecu, so that it gets better signals and responds quicker and more efficiently
HTH
Paul
Thanks Gix, I had a look at the website, and I guess for the money, it's a cheap enough mod, that can't do any harm. I suppose at the very least, with some nicely coloured cable covers, it'll look bling in the engine bay
agree on that one mate