I feel naked without a mirror. Don't like surprises coming from the rear. Even in group rides a mirror helps with tracking other cyclist.

I too use the Take-a-look mirror, have this mounted to sun glasses. Properly setup, small eye movement provides a rearward view. A helmet mirror could do the same, but I have multiple helmets and one pair of glasses.

One bike has a bar end mirror, but it's not that effective. The distance from the eye keeps objects smaller plus it's not as clear that far away. And, I'm always adjusting my position to check out the mirror. I also see people with helmet mounted mirrors shift their head to see the mirror, too, perhaps these are not setup correctly.

Anyway, the take-a-look makes it simple and easy and provides great visibility behind you.