The list of companies that accept Yubikey as 2FA is quite large and it includes brokers like Kraken and Gemini (as well as Google, Facebook , Tesla, Teamviewer, many Linuxes and a bunch of others) https://www.yubico.com/works-with-yubikey/catalog/ This could be a better than the option of mailing physical cards to people. It also more convenient than having to open the app everytime. Sometimes the app option (to put the fingerprint) doesn't show up and I have to type out the numbers manually, this would remove that hassle