I didn't like the way the Oberon-style mirrors I had weren't adjustable on-the-fly. If your riding position is constant, that wouldn't be too big of a deal.
Plus, I where I live everyone's always grabbing my shit at stoplights or while the bike is parked and saying "What is dis? How much cost it??" so eventually someone loosened a bolt tugging on it and one of my mirrors subsequently fell off while moving.
Then I picked up a set of the clamp-on-over-a-little-bar-plug kind which a plastic ball joint attached to the stem for a small round mirror, like Drewski shows on his bike.
Nicer, but the cheap-ass copies I ordered off Amazon started getting loose pretty quickly and required continual snugging-up. (Abetted again by the "everyone feel free to handle my stuff without asking, especially something that looks different than what you have" mentality here.)
Just sheared one off on either an autorickshaw or a bus, though, so I'm glad I only dropped $15 on them. They actually function more as sacrificial antennae than mirrors for me.
Using a Napoleon-style square mirror on the new bike, if I go with a mirror at all. Not too useful for me over here.