Security keys like YubiKey, Solo Key (with or without Nextcloud)

Anyone have experience with using security keys like YubiKey with or without NextCloud?

Or has anyone seen this KickStarter for the new Solo Key? Any thoughts?

Was thinking about getting a YubiKey when found this KS campaign for the Solo Key.

I can see that using a security key with a website that supports it would improve security.

But would using a security key to access a password manager to get to websites that do not support the security key offer any security benefit?

Below is Wikipedia article on YubiKey with list of support services/platforms near bottom

Thanks for any comments.

I have used Yubikey with Nextcloud, via OTP and via U2F. Works quite good. It’s nice to have different modes and also use certificates. If it is just for U2F, there are a few other and cheaper devices.

I would appreciate if anyone can comment on which 2FA-related alphabet-soup anacronyms Nextcloud 14 supports (eg. FIDO U2F/CTAP1, WebAuthn, etc), when using some kind of Yubico-like dongle, (which might also have NFC, for use on mobile devices).

Please dispel the perplexity on what will and will not work, at present!

I have the Solo key, and it works fine both with the U2F and the Webauthn app. I am however still looking for a passwordless solution.