I agree, Tesla's Autopilot should not be used on secondary highways. It's obvious from "Tesla tried to kill me" video that user interface is not fast enough to handle winding roads - with no shoulder or median - at high speeds.
And I don't agree.I live 40 miles from freeways. Most daily driving is on secondary roads, not even highways. They get long and tedious, too. The Tesla AP handles them well.
I drove on two lane winding roads for a couple hours yesterday. Of course, with autopilot, cruise was on. Car was going fast, but handled the corners, although abruptly. It was obvious that I could see the curve better than the radar, before the radar, and when the car recognized the curve it had to do abrupt steering. Simple fix was to slow the cruise control down. I never had to "grab the wheel".
When following a car on two lane curvy road, there were no issues.
Car recognized that guard rails, bushes, cars, flat bed trucks, were beside me. It never dodged anything. I exercised confidence and let it shy away from things it wasn't sure of, but that was rare and I never had the feeling it was "trying to kill me" which is a bit much of an overstatement. My Mom likes to say things like that to be sensationalist, so I'm used to it. It had to feel its way when the center lane moved away to make room for a left turn lane, but quickly figured it out. ONLY ONCE did it ask me to take over the wheel on a section of curves. Usually it could find one side or the other of the rural road and follow without trouble.
From my understanding, each car that autopilots down a stretch of road collects data. Then all later cars will understand the road better as data is collected about that piece of the map.
I feel strongly that new AP drivers should start in slowly and learn with the car. Don't push the envelope until you are confident, and you will have nothing but a great experience.