Cons: there may be a focusing issue for elderly cyclists
The idea is brilliant and it will work for most folks, but I was forgetting how eyesight changes as you get older - I am now an OAP - and even with varifocal glasses on, I could not focus down to the mirror, which was only 200 mm away from my eye! This won't be a problem for youngsters with flexible eyeballs! In the end I kept the Zefal (useful for looking into small holes!) and bought the Mirrycle MTB bar-end mirror. This is a great product, very well made and does the job perfectly - highly recommended and certainly much better than the Zefal for me!