I've used a helmet mirror for many decades of riding, and I recommend a mirror for anyone riding on the roads. Being visible is important, but you can be hit by someone behind you who is looking at you. This happened to an experienced friend recently. The driver stopped and called 911 and admitted that he saw my friend. I managed to avoid something similar by moving onto the shoulder when I could see that the car wasn't moving over to pass me. The car swiped me and knocked my pannier bag off, though. The driver did stop to check on my, and said that he saw my tail light (this was at night on a quiet road). Most people are competent drivers, but some make mistakes. Cyclists should not trust them, and a mirror lets you keep an eye on the ones close to you.

I also use a Take a look mirror that is easy to attach and remove from my what ever glass's I am using. They are only $25 and offer a very big view to whats behind me. They are very helpful when navigating across multiple lanes of traffic while never having to look over your shoulder. One of my riding buddies has the same Tri Eye and he loves the results but some of us need optical lens. Both styles of mirrors are a great addition for cycling, plus. After all, all motor vehicles rely on simple mirrors.

Garmin Varia...expensive, but worth it.

yea, not replacing my sungods and helmet mounted mirror for this lol.

I currently use a take a look mirror with $5 Temu photochromic glasses which work perfectly but this looks way cooler. I have ordered some.

Does it have an attachment for prescription lenses?

Garmin Varia is a game changer. 100%

Can you put them over your normal glasses you wear

Apparently he never considered eyeglasses with a mirror for overcast days (you can get lenses without correction).

You can also train you ears. Number of vehicles, size, distance are all obtainable.

Nothing comes even close to a rear view mirror. But they don't make ones which sit further out on the hoods. That's the position where you don't have to take eyes off the road or bend your neck, and the most safe unlike the mirror on drops.

They also have rear cameras to attach to bike