I use the Take-a-look glasses mirror most of the time, but I installed something called "The Italian Road Mike Mirror" many years ago on both Left and Right bar-ends for additional coverage/backup.
PROS: High quality, robust (never scratched or broken one), aero, light, no vibration, absolutely stays put, doesn't look "Fred"
CONS: You need to remove bar tape to install, minimally adjustable, a bit expensive ($45ea), requires fiddling / re-taping to get it aimed perfectly.
In summary, it's initially a pain to set up correctly, but then it just works forever.