This product was recommended to me by Don Shillady, master chemist and unruly teenager.
If you buy a gallon, the freight is paid, so the first oil change will cost you $6.90 (7 1/2 ounces of the product added to the engine oil) and subsequent oil changes will add only $4.60 (5 ounces of the product added to the engine oil) to each oil change. Pretty cheap insurance, I'd say.