I am in the process of switching all of my tractors, semis, vehicles and anything with a motor to Schaeffer's fluids and grease. I am partial because my brother-in-law is a rep, but after his demonstration, I was sold. He also has been using it for 30 years in his personal vehicles and race cars.
There is a local trucking company and shop that has a 6.0 Powerstroke master that is going to do some work on my 6.0. They run 37 trucks and that is all they use. They are getting .5-1 gal better fuel mileage and dropping the oil every 40,000 miles instead of every 10,000. Schaeffer's is big on testing fluids before you switch and during use. You just have to buy the test kit for $6 that come with a prepaid shipping package.
Like others have said, it is a personal preference and there are some other good oils out there. It is definitely worth checking out though.