I’ve had a couple different bike mounted mirrors. The Mirrcycle one is very good, but easily gets banged in the garage and at bike racks. (US-made, too) All the other bike-mounted mirrors were junk.
I have the compact Bike Peddler Take a Look mirror that clips onto one’s glasses. It’s OK, but fiddly and too close to the eyes. The original might be worth a look, if you really don’t want a mirror permanently attached to your helmet.
This is the one I like best so far. It too is Made in America. Unlike other helmet-mounted mirrors, this one doesn’t use adhesive patches, but either zip ties or Velcro straps. The articulated stalk holds its shape well and doesn’t vibrate. It’s called the EVT Safe Zone Bicycle Helmet Mirror on Amazon, and I bet you can buy it direct from the mfr. too. View attachment 12060View attachment 12062
The packaging says it’ll work on any helmet, but it won’t worm on my ski helmet unless I drill a couple more holes for another zip tie.
I paid $40 on Amazon; might be cheaper direct from the Mfr.
I have been using this mirror for a while now, and I have to say that it's excellent. I installed it using the suggestions above and some adhesive velcros and two cable ties and really no problems at all. The only possible improvement could be a mirror with a slightly wider field of view but this would give a wrong distance feeling.