I have a Tesla and have tried FSD several times (month-to-month plan and loaner cars from Tesla). It's comically bad. Fortunately every time I tried it I was paying very close attention so I stopped it from braking at green lights, trying to turn right from a middle lane, halfway lane changes where it snaps back to the original lane unexpectedly, etc.

The regular, included autopilot works pretty well as a smarter cruise control; as long as you use it on a major highway in the daytime in good conditions it does a good job. And it's very useful in stop-and-go traffic on the highway.

But the FSD is crap.