Installed 18.12 and attempted a local road which has a few 20 MPH dogleg curves. At set speeds of 25 to 30 MPH, the car was okay in one direction, slowing slightly 2-6 MPH in the turns. However, reversing the route, it ran on the double yellow lines and I had to disengage due to a bad road surface between the lines, and in one case due to oncoming traffic and I wasn't comfortable running on the line.
This is the first time I've had the MS on this road, so can't compare with earlier releases. However, based on earlier releases on other roads, there is no way I would have trusted AS on this road in the past. I have a really good feeling about 18.12 and have to run it on my test highway with long sweeping curves which prior releases hugged the lines at speed.
One major change I noticed with 18.12: Usually AS couldn't be re-engaged after a disengagement for a few seconds, however I was able to turn it back on almost immediately. Needs more testing on all road types.
I have video but have to clean it up some before posting.
I can't speak to the navigation changes with 18.12 as I relied on Waze in the past, because, well, you know...