You may like your turbo kit, your intake, or your muffler but this sticker is the most important thing you'll need. It's the little self-stick nothing that lets the police know that they've got nothing on you. The part on your car has been tested and is emissions legal for use. No fix-it tickets, no impound, no attitude. Now, not all parts come with this sticker (this one is for a HKS air intake system) but there's a reason why the real, tested, emissions legal stuff costs more than the knock-offs. Don't be cheap.