I’ll second this, it’s absolutely a game changer. I’ve used handlebar mounted mirrors and the like but I’ll never willingly go back.

I tend to prefer helmet mounted and I glue them on which isn’t my favorite thing to do on a new helmet. It’s also a bit frustrating when you find yourself cycling in a country that drives on the opposite side.

I do find that on very long tours the week following I’m looking where I’d expect the mirror to be when I want to look behind me.