I haven't had a good experiencing with Yubikey's support and sales team and I'm looking for an alternative.
What other keys are people actively using?
I'm interested in something with equivalent features to the Yubikey 4 (NFC not required, U2F mandatory).
Open source (-ish?) Yubikey alternatives
https://sc4.us/hsm/ $75 | https://news.ycombinator.com/item?id=12053181
https://trezor.io/ $99 | https://news.ycombinator.com/item?id=10795087 (not much on HN)
https://www.floss-shop.de/en/security-privacy/smartcards/13/... €16.40 (OpenPGP Smart Card v2.1; 4096-bit keys)
https://www.fidesmo.com/fidesmo/about/privacy-card/ €15 (NFC only; recommended by the terminated SIGILANCE OpenPGP Smart Card project; 2048-bit keys)