I have done a lengthy test of using Marine Spec TC-3 2 cycle oil. Mixed at 1 oz/5 gallon. There is a big thread on it here:
Been testing - LS1 Performance Information
My results on fuel economy are inconclusive due to the climate change as I got into my fourth and fifth tank. However, my escort idles noticably smoother. Fuel pump is a lot quieter. And it is definitely easier starting. It is basically billed as a top end lubricant and fuel system/top end cleaner.
I've been using it in my fourwheeler, and it is SO much easier to start now compared to what it was. Now it will start after about 3 or 4 turn overs, compared 7 or 9 before. It was getting to be a bear to start in cold weather.
I need to break down the data in fuel logs and see if I see any trends in there for sure. Just glancing at them again, it appears there may be a decent increase in mileage trend. I wasn't using it for mpg, but for top end cleaning/lubrication.