For the Tesla driver assistance specifically (non FSD) it's more advanced and reasonable reliable. I find it helps a great deal to reduce fatigue on long drives. It is nearly flawless on highways and watching to see the car is safe is much less fatiguing than a constant centering and monitoring the accelerator. Seeing the car is the right speed is less mental energy than constant control of power to get the right speed
Given the potential consequences of a mistake, it feels like there's still a pretty big difference between "nearly flawless" and flawless.
Speed control I'm fine with and is obvs. a mature tech that has been around for decades. Maybe it's the way I drive, but I find lane assist a liability -- especially on curves. More than once the car swerved unexpectedly one way or the other going around a bend. After the 2nd time that happened, I shut it off.
I suspect the difference in experience might be attributable to differences in the environment. I went cross country in a model Y and noticed that it did not handle one lane turning into two lanes with any grace - but I also drove across entire states where that didn’t come up. It wouldn’t surprise me if some experiences were regional to an extent.
Lane assist isn't supposed to entirely keep you in the lane on it's own, it's supposed to just help tug you in the right direction as a hint in case you weren't paying perfect attention. It's usually not supposed to steer the car entirely on its own.
You can’t really concentrate for long times, and as it has been shown many times, people are bad at expecting rare events. Reasonably reliable is not enough.
