I demo'd one the other day. Running on my A300 bobcat, it performed about as well as my Rayco 1625, and the teeth were pretty beat up on it.
My a300 does not have the high flow option, and I felt that the stump grinder attachment was supposed to run on the high flow; it seemed like the wheel was turning a little slow.
Summary: the visibility was very good, since you look at the side of the grinder wheel. The hydraulic controls were very smooth and slow, allowing for genuinely easy grinding. Maneuverability was quick and easy, and positioning on hillsides and moving from stump to stump was MUCH better than my Rayco 1625.
A really cool feature: the stump grinder attachment has a solid steel skirt that provides much better containment of the chips. After the stump is ground, you can bulldoze the pile back where you want it.
Overall: it is as good as a 25hp stump grinder, with some added strengths that can't be matched by the smaller stump grinders [Air conditioning comes to mind!] On the other hand, it simply won't go all the places the smaller stump grinder will go, and it's not very practical to haul 9500 lbs of stump grinder to a job unless there are a lot of stumps in one spot.