I've been using a bar end mirror for a good 10 years now and wouldn't ride without it. One additional positive aspect I've not heard anyone mention is that it allows me to ride farther left in the lane most of the time, and move to the right only when I see a car approaching from behind. It really seems to cut down on the flats to only spend ~10-20% of the time to the far right and ~ 80-90% in the center right of the lane. As an added bonus the drivers see me "owning" the lane but ceding it to them by drifting right as they approach, then moving back over after they have passed. Makes them realize that I have a right to full use of the lane and also increases my visibility to them.