But currently not very popular.

there are millions in the wild ... so maybe not super popular but it's above penetration of anything you would call a niche product

Millions in the wild, but mostly sitting in a drawer.

https://www.wsj.com/tech/personal-tech/metas-ray-ban-smart-g...

That's about gen 1, gen 2 is vastly more successful

Is it? I've seen zero people wearing them in central london.

I haven't noticed anyone wearing them in real-life, despite walking every day in a concentration of university/college campuses (Harvard Square, USA, and surrounding neighborhoods, sometimes including MIT).

I've only noticed some influencers wearing them in Web videos, where they look prominent, like I should also be able to recognize them in-person.

Maybe people are only wearing them at home or in the office? Maybe it's mostly a California techbro regional thing?

Maybe I'm not paying enough attention. I will start consciously looking for them.

I've ever seen them in the California Bay Area either. I don't go into the office for my current job, though, so maybe there are some tech bros out there wearing them?

That's a pretty small fraction of the population.

There are about 50M foldables in use, probably 30X as many in use as the Meta Ray-Bans, and I see one of those every couple of years and the only pair of Meta Ray-Bans I've seen in the wild has been a blind friend who got the first generation early because of its accessibility capabilities.

I got given them for free and I've never once turned them on. There's no way in this world I would ever wear a Meta produced personal life tracking device on my face (or anywhere else for that matter)