I have one but to date have not seen any EVIDENCE that they do anything, and was having this very discussion about my one with someone very knowledgeable, who said it was his opinion it was another gimmick, and would do nothing to very little, or a turbo car such as cossie.
I ammin two minds wether to us it or not.
Would be interesting to hear and see any before + after printouts though.
tabetha