I use a helmet-mounted mirror. Very good since i mounted it on the helmet.

My old helmet didn't have a visor and mounting int on my glasses was less ideal.

Problem with bike-mounted mirrors is that if you lay your bike down it gets damaged. Or if your lean your bike against something.

With helmet-mounted you also can rotate your head a bit to see around.

Just my 2ct. Others may have good reasons to favor bike-mounted mirrors.