With a tow dolly, you will still need brakes, and a light package (either tied into the vehicle, or magnetic type that are placed on the trunk or inside window).
If you know that you will be using the Fusion as your toad for the next few years, it may make sense to go with the 4-down, as it's much easier to operate once you have it installed....taking a couple of minutes to hook-up, compared to all the work involved in putting the car up on the dolly.......a big thing, when it's raining out:(
I will probably go with a dolly myself, but because I want the ability to tow different vehicles, depending on what we need for a particular trip.
Your diesel should have no trouble with any option you go with!
Happy Camping:)