Duo Free used to have a restriction of one device, but it seems for U2F they now require one of their paid plans: https://duo.com/product/trusted-users/two-fact

Duo Free used to have a restriction of one device, but it seems for U2F they now require one of their paid plans: https://duo.com/product/trusted-users/two-factor-authentication/authentication-methods/u2f https://duo.com/product/trusted-users/two-factor-authenticat...