I have had helmet mirror but found it hard to keep aligned, and fast descents would make the mirror shift. I have switched to eyeglass mirror. I wear progressives both regular and sunglasses. Works great. If you can use your drivers side mirror in your car, you can use eyeglass mirror.

Another point to consider - you lay your bike down on the left side (non-drive side) - thus a handlebar mounted mirror is more susceptible to damage. Also any crash will likely destroy a handlebar mounted mirror.