My only issue is the ... unclarity... with them.

The option pops up in the middle of a normal log-in flow. I'm guessing most non-techies don't know how it's implemented.

Oddly, some login flows display a normal user/pwd form, but you get the in-browser "use a passkey?" option/popup which further confuses matters.

Thankfully, me, wife, and all our parents are tech-savvy enough to use password managers, so the fallout from lost passkeys hasn't be an issue. But I certainly see how it would be an issue for anybody entering passwords from memory or similar.