Black Bud

You still want to know where the traffic is that's coming up behind you! Your ears won't tell you just how close that car really is (not enough distance between you and them in practice) and one little mistake can be fatal.

Now, mirrors for bikes do have their disadvantages: Helmet mirrors tend to be delicate, difficult to keep in adjustment and allow the rider to develop the BAD habit of looking up and away from where they should: In front and around them. Which is where everyone else tends to be (it's very unlikely your next road hazard will be aircraft).

Handlebar mirrors tend to be more robust, but can be a pain to fasten properly to the handlebar (almost all of them use "quick release" mountings) and then stay where one wants them to (the mounts may not clamp the grip firmly or even fit over the grip without a bit of "adjustment" from your friendly, local set of pliers ). They are also prone to distortion of the image from vibration (road shock--which one can learn to compensate for) and/or poor optics (which cannot be dealt with by the user), so choose carefully and be prepared to replace the mirror when necessary.

So it's easy to get that "view of what's coming from behind" for people who use bikes with "flat" bars or other bars that can accommodate the "mountain" style mirror.

However, if one owns a road bike and uses drop bars? Good luck finding a mirror that will work for you, although if one rides in the "heavy load touring" style (uses the drops but rarely), this is not an insurmountable problem. The biggest problem is finding one to fit: Mirrors designed for drop bars are not common, although Blackburn offers a good one that has a wide viewing angle and mounts easily to the hoods. The biggest problem with the Blackburn--if one runs brifters--is that the action of the brifter lever (for shifting purposes) can be impaired if the mirror is strapped on too tightly (the mounting strap is quite wide and can interfere with the mechanism).