I have one of the mirrors you describe and have had it for 3 years. They do not drop off, or at least mine doesn't, but I do find that if the sun's rays are striking the lens you do have difficulty seeing anything. Normally you can see closer
to the rear of your vehicle that you can see through the rear window but not close enough to view the towing hook. It is still difficult to estimate distances and I wouldn't trust mine when parking. Hope this is helpful. brian.f