This auger is FANTASTIC! It has plenty of power--if it hits a large rock, I can just barely keep it from spinning me around. It handles small rocks, clay, and small and medium tree roots without issue. Obviously, this auger isn't going to pull a rock the size of a grapefruit out of the ground, but it has cleared rocks that are baseball size and smaller. The motor hasn't overheated or given me any problems, even with hard use and a very aggressive duty cycle.
I'm also very impressed with the auger bit. The narrow pilot has a carbide tip on it, and the leading edge of the blade is reinforced. I have bored several, several holes, and the auger doesn't show any wear except minor paint rubbing off. I think this tool could do thousands of holes if I needed it to.
I'm so glad I bought this, and don't have to mess with a noisy 2 cycle engine that's going to need a part every time I go to use it. This auger is completely maintenance-free, and I find myself using it more often because of this.