Every highway in California, pretty much. It does not “move into” any lane, so I’m not sure what you’re referring to. When there are no lane markings, it follows the car ahead of it. If neither is present, you nudge it where you want it to go until either is present again.
It doesn’t “require attention” every 15 seconds… it requires attention at all times, as it isn’t a hands free system and no such system exists yet on a road-legal car in the US (certainly not Tesla). I’ve had no issues with keeping my hands (or a hand) on the wheel.
Works great on curvy roads. I’ve used it on CA-17 to Santa Cruz with no issues, and it’s extremely curvy.