A HUD reduces the difference in focus distance between "looking at road" and "looking at speedometer." It matters more as you get older, because your eyes focus slower.

Yep. My new car has a digital rear view mirror. You flip a switch and the rear view mirror becomes a screen showing a feed from a camera on the back of the car. It’s nice for night time as well as when the rear window is blocked by rear seat passengers’ heads, or cargo or whatever.

But it’s uncomfortable for me because it requires my eyes to refocus from distant to close and back when I glance at it, which isn’t needed with an actual mirror. So I don’t use the feature.

Somewhat unrelated, but this discussion made me go from "I don't see what I would need something that tells me tomatoes are tomatoes" (though realtime translation looks very useful), to kinda wanting it only to have a figher plane HUD-like display all the time (to be clear, minus all the fighting parts). Almost useless (at least the attitude and vertical speed part) but would feel kinda cool. Can see some value in having the heading all the time, and speed display to motivate myself to walk faster. (well they have directions which provides much more value than all that).

Though I don't feel comfortable having more Meta in my life.

If you have a nice old-fashioned speedometer you don't need to read it, you can just glance at the angle which will work well for poor focus.