You sure as heck don't need a Jake brake. They are nice to have I imagine especially with all the extra weight of a DP. I still have to fight the urge to pump the brakes in a hard stop even though I have had ABS systems for years. Rgatijnet1 makes a darn good point about reliance on a system like that.
If someone has no idea how to downshift and pick a safe speed to descend a steep road, then they would benefit from an exhaust brake setup greatly. The newer F-53 chassis with tow/haul mode overcomes this as well by forcing a downshift when the brakes are hit. You can overheat your brakes on a passenger car on some grades if you don't downshift.