Good review on mirrors
The link above is a good read for considering mirrors. I tried the Third eye mirror but did not like it. The mirror was too close to my eye to use comfortably.
So I tried the Take-a-Look mirror. I like it much better. Been using it for about a month now. Easy to adjust and stays put for me very well on my glasses. I never tried the helmet mount.
As for those that say they look dorky, do you realize how dorky we all look wearing spandex?
Adding a mirror is not gonna make much of a difference to how you look on a bike