I bought a helmet mirror from ebay for less than $3. I have been using it for 2 days now. I am not sure how the expensive ones performs or do they give you a better view. But for the one I got, when I set it up for the hoods, I can't see what's behind me on the drops. And you have to train your eyes to get used to seeing what's behind you. Bottom line, it's not like a car rear mirror.

Being able to see what's behind me give me chance to relax a bit if I know there are no cars behind.

However, do you guys really feel/think having mirrors improves safety? I am thinking if cars want to hit you, they hit you regardless of you having mirrors or not.

Are you riding any differently with or without a mirror? For me the benefit is noticing no cars behind and ride more enjoyably.