I use the Motorcraft stuff now and then. I buy a case and grab a bottle every couple weeks. Have I noticed or measured a difference in MPG or performance? No, have not seen any real benefit. It's purely a leap of faith.

I don't use it all the time, I generally buy more than 300 gallons of diesel every month so it never sits in my tank and I would go through tons of the stuff if I were consistent with it. Every time I fill up I view it as a very temporary situation with the fuel I just bought.