Don't waste your money. If your car's primary voltage is severely out of regulation due to a charging system fault or a bad connection(s) then the car will not perform properly and fault codes will almost certainly be triggered. Same if there are ACTUAL defects in the secondary ignition system. Otherwise, the car's engine management electronics are designed and tested to perform stably in the face of any reasonably expected voltage variations. No halfway or better competent engineer would design them any other way. Besides, at least in the USA, EPA emission durability standards mandate tests that essentially guarantee this.