I dont have the fm100 pre-filter, I'd have to run two fm100 heads to do so. My filter on the fm100 is a 2 micron so I figured that a separate prefilter would be prudent, and the racor is very cheap and very high-quality
The prefilter is totally optional but I think it's a great idea if you plan to run a very small micron main filter like the 2 I'm running.
The clear fuel bowl is a nice touch and is a great indicator on when you need to swap out the filter (if you didn't mark it and forget) it's easy to see with a flashlight any garbage that made it to the filter head and makes water and Alge easy to see
Two other options are the hand priming pump on top (I've got this) makes filter changes and printing the system really easy as it works much better than the lift pump priming handle. They also make a fuel heater, you can wire this to the glow plug circuit and it will warm the fuel before starting the truck or you can run it constantly in artic conditions (fuel lines would also have to be heated but that's another thing)