Fuel Separation Systems

Is anyone here familiar with fuel separation systems like Fass Fuel? What does it do for diesel vehicles?

I don't know much about that system in particular, but the benefit depends on the corruption of the Diesel fuel in the tank.
I expect if you fill up with fresh fuel it will be contaminant free - and you'd see little or no benefit.
If you rarely drive the truck, the fuel will absorb water and may get other contaminants in it (rust flecks from the tank, etc) and after several months would see a benefit to a filter & water separator.
Many Diesel engines already have a water separator and filter, however.