I never got used to it.
First of all a "blackburn" helmet mounted one was so wiggly, that I couldn't see anything. I now have a "take a look."
It takes me a few seconds to shift my focus, and place my head at the correct angle, so I can actually see out the thing. That's too long. A glance down to my bar mounted mirror is easy and works. A problem is that most of my riding is in town, so I'm constantly turning my head, not riding in a mostly straight line.
If there's hope for getting used to it over time, I'll give it another try. Maybe I'll wear it around the house. There are analogous situations, for instance some people have a very hard time getting used to looking into a microscope, or VR goggles.
It would be great in the supermarket, or in my kitchen.
