Well the DR walk behind isn't too bad on moderate terrain if you just work for an hour or so and the terrain isn't too bad. OTOH, I've taken mine to work on state forest bridle trails and it wore several of us out taking turns operating it. But it sure beat clearing by hand!
It's kind of funny, when I got mine, everyone was enthused about it and a few others were purchased. Now, no one wants to take them to work on the trails, a skid steer operated brush mower is preferred and a forestry mulcher is what is lusted for!
The tow behind is only good for semi cleared trails since the tow vehicle has to be able to drive ahead of it. The walk behind works for clearing areas that are too overgrown for a tow vehicle. In my experience, a 400cc ATV is marginal or inadequate for pulling the tow behind.