I've had two cars now with head-up display info on the window. It shows speed, adaptive cruise control status, lane keeping, maximum speed, navigation info and warnings. I will definitely get it again on any future cars. It's so much easier than looking at the displays inside the car.
A small but well thought out safety future using the HUD is in the dark, when the car detects a pedestrian or cyclist on or moving into the road using the infrared camera it will show a yellow warning icon. Has shown me people walking in dark clothes on dark rural roads a few times far before I could see them myself. This is a video of the detection, mine doesn't have that spotlight, but shows the warning on the window instead: https://youtu.be/WpB8ZLGq7EE