I am totally sold out on the use of mirrors. Commuting, or road rides.
Commuting it simply makes sense - what is coming up behind? Although I use the mirror for a quick look - before I make a lane change or turn I will still look over my shoulder. Gray cars in the early morning or fog with no lights, all too common and they disappear in the mirror.
On road rides, they are handy to see coming what you cannot hear. Last road ride with my wife we needed to dodge up a driveway a bit, since the cultivator driving down the road was overhanging not just the fogline, but the ditch by some several feet. Fun thing is many of the farm equipment drivers are about 15 or 16.
I may not be cool, but I have rarely been so accused anyway. And too old to care.