UPDATE: It worked very well, but it was often more stressful than just doing the driving myself. Sometimes I had a cliff on one side and a rock wall on the other. It probably wouldn't have caused a crash, but I usually intervened.
Sometimes it seemed to be going into curves too fast, and other times, it slowed down way too much. I had it on about 40% of the time, but I always had two hands on the wheel. I called it "riding the wheel."