I've been playing with it since I got it a few days ago. I love the visualizations, but obviously it's not ready for primetime at all. I'm okay with making sure the steering wheel does what it needs to do, but the biggest flaw to me is how it treats forward traffic. I had the gap set to 7 car lengths on a 45 mile an hour road, and it was following more like 3. I turned it off and used autopilot and it was much better.
Similar situation last night, engaged FSD when I saw that my street was backed up with traffic. The car jumped and sped up instead of just coasting in behind the car in front. I had to disengage right away, completely freaked out my wife.
That's that, I'll be using it only when I'm driving alone and ready to teach the car. Definitely made me appreciate how well regular autopilot works.