Speaking as an experienced Stump grinder, my advice is don't try it yourself!
These things are lethal potentially, and you really do need to know what you are doing. Flying debris is a major risk, I've been hit in the face once, and hit in the legs countless times.
The pedestrian type ones also have a habit of lurching forward quite violently. Plus all the other stuff like buried cables/pipes etc. Definitely a job for the pros.