You should probably reach out to Baumalight, it's a cat 2 implement, so the first question will be, can your tractor lift it? Beyond that, honestly, I think HP is just basically speed with this cutter. If you can lift it, you can use it, just will have to go slower. It's all about getting those blades up to speed, once they are spinning, actually impacting a tree to cut it puts almost no load on the tractor. Grinding it up, like you see me do in the video, puts some load on my tractor, but it's nowhere near starved for power. Now, if you put it in the dirt, you'll feel the power, for sure. That lugs the tractor mightily. But actually using it for what it's intended for (IE, not a rotary style rototiller), I'd think you would be OK with less HP than I have (60, ~45 or so at the PTO). Let me put it this way, I can cut faster than I can position by a pretty significant margin doing what I'm doing. Now, if you're just going dead straight and eating trees as fast as you can, yeah, that will become HP limited, but I also can't think of many situations where you'd be able to do that (maybe a very grown up right of way?). For clearing underbrush, you'll spend as much time with nothing under the blades as you do actually cutting a tree, plenty of time to recover the RPMs for the tractor and machine.
I think that is the case with a solid 50% of my implements. I wish a 3pt/PTO in the front was more common, there are a lot of tools that would work better that way. This this would be beyond awesome if I could hook it up in the front on my FEL! Of course, then I'd need hydraulics to run it, which I could get from a PTO in the back, but it would be much more expensive. If my tractor just had a front 3PT and PTO, I'd use it at least a significant minority of the time; would be very useful.
