how do you know it doesn't void warranty?
I always thought these chip tuner's voided warranty??
800-900 is a good price though i think!
I think most of them just plug in to ECU, they overide stock settings, they mostly with a diesel put more fuel in to gain performance. as thats how diesels work, more fuel more rev's. with petrol you give them more air.
but the one's i have seen on diesel's without the CPF ( filter in exhast pipe ) they tend to blow more smoke. what i would worry about is that it might overload the filter in the exhast and cause problems with that.
but about warranty and not voiding it, i think you just unplug them before going to dealer for work and no one knows it was ever there.