I have used it, I did some fairly comprehensive testing in my 95 PSD about three years ago. I tried it at 1 oz per gallon, 1.5 oz per gallon and also up to 2 oz per gallon (along with my usual dose of DieselKleen or Howes) and all I came up with was inconclusive results when compared to running with straight fuel and an additive. Some tanks showed a slight increase in mileage and some showed a slight decrease in mileage. As mentioned, inconclusive.
Its just not worth the hassle IMHO to mess with this stuff (especially if you consider that a drop or two gone unnoticed on your paint will eat it off) when I can get better results with an additive and an ounce of 2 cycle per gallon.