Helmet-mounted mirrors ARE--almost--worse than useless, IMHO!!

I used one, briefly, before I found hood-mounted ones for my road bikes. The mirror was tricky, at best, to keep in adjustment and picked up way too much vibration to adjust to..even breathing would make the image "jump"!!

Handlebar-mount mirrors work far better!

Are handlebar mounted mirrors perfect? No! They will pick up more vibration, and need more adjustment, than the ones on your motor vehicle...likely due to the 'removable", and lightly-built, design needed to make the units usable for cyclists. A well-designed one, however, will minimize these problems.

If a mirror is used PROPERLY, you WILL get more than 0.1 second warning that a vehicle or vehicles are coming up behind you...you should get enough time to react accordingly! ALSO... and I have said this before!... a mirror is NO SUBSTITUTE for that head turn!

YOU NEED TO DO BOTH !!