I've finally gotten the hang of the helmet/visor/glasses type after quite a few failed attempts with mirrors of different sorts.

My favorite at the moment is the Bell Metro visor mirror which doesn't seem to be all that popular. Works for me anyway.

The Take A Look is probably the best. It's certainly larger than most. I like being able to fold the mirror up out of the way and the smaller overall size of the Bell personally.

The best thing about mirrors of this type is that you can keep an eye out for cars substantially further back that may be closing at speeds considerably in excess of the speed limit, IOW the sort of drivers you might want to look out for.

They don't replace looking over your shoulder. They just give you another option.

The quality of viewing is down to how well your eyes work.

I can't really focus on anything too clearly. But, I can see well enough to have an idea of what is coming up from behind.

It is worth acclimating to them IMO.

I'm not comfortable with any mirror I have to look down at to use. That rules out any of the mirrors that attach to the bike in one way or another for me.