I don't know about you but there's the occasional bump and pothole in the roads around me and it takes very little in the way of bumps or vibration to knock this mirror off its setting. Even set so that the mirror hangs more or less vertically so that the mirror's weight has very little mechanical advantage over the friction of the the adjuster, it bounces out of line with very little provocation. The result is that you are constantly having to reach for it and line it up again.
Second problem is that the oval shape means that despite the wide angle nature of the mirror, your field of view is limited.
Poorly designed and only of any use if you cycle on perfectly flawless, velvety smooth roads.