I have done the alternator "rewire" and later the volt booster (stage 1). I can say for sure that my headlights were increasingly brighter after each of them. Some have said there were some improvement to the idle and tranny shifting. I think I noticed the same thing. It was minor enough that it could be placebo, but in the end I was happy with it. Peace of mind if nothing else. If you are resourceful you can do both on your own for cheap, but it was just easier for me to buy them pre-made.