Someone from costa rica made one to do like 2-3" growths of something like bamboo that could be coppiced. They said it worked well for their purpose. I kind of like the design because it is a bit less energy intensive, it self-feeds, and it operates at a bit slower of a speed. It is harder because you really want a pretty accurate screw, they are harder to sharpen and keeping it in adjustment can be trickier.
If you want a good analogy, it is kind of like reel mowers for lawns. If they are tuned in, and the grass isnt super long, they are really great and they cut better then a rotary. If they aren't tuned in, or the grass is really long, they suck.