Does Mileage Maxx work?

My wife and I went to get our car serviced today and were pressured by a salesman to purchase a product called Mileage Maxx Mileage Booster. He told us that it would clean out our engine and increase our gas mileage by quite a bit. It wasn't too expensive, so if it actually works, it would be worth the purchase. Can anyone tell me if they have actually used this product?

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