Hello Jack
Yes, if you plan a route on the DMD2 you will be routed, but to be honest the routing on Garmin works much better and the calculation is much faster than on the DMD2. But that’s not the reason why I still prefer to use DMD2.
DMD2 focuses on off-road riding and also offers an easy way to get to the starting point of your GPX track (admittedly less well than with Garmin or Google Maps).
Advantages from my point of view:
DMD2 has a more pleasant interface for my purposes.
I really appreciate that I can control DMD2 with my handlebar controller while riding.
I like the ability to show OBD2 data on my display.
The advantages of DMD2 over a pure Garmin solution were so great for me that I sold the Garmin Tread Overland and have been riding with the T865 ever since. The system is much more flexible and I can use almost all Android apps.