There has been past discussions on here and others I talked with. For a gas engine, save your money. They do little if anything to improve mileage or performance. But each case is different. Some do well with exhaust system and air filter upgrades. A better chance for specifics would be to Google your engine.
You could try some searches on here but since this forum has the world's 1st or for sure worst search engine, I doubt you will find it.