A tuner of this sort is something that I want and need for my car. The S-AFC is good for what it is (knowing the limitations of a MAF tricker), but I'd love to be able to adjust spark timing as well. That said, I would go from shop to shop locally and conduct interviews beore I let any tuner touch my spark timing, and get a signed liability document before anyone got their hands on there (that is, if anyone was actually willing to do that).
