That depends on what methods of authentication you want to use with your hardware key.
The Security Key C only supports FIDO2/WebAuthn (hardware bound passkey) and FIDO U2F authentication protocols.
The 5 Series supports FIDO2/WebAuthn (hardware bound passkey), FIDO U2F, Yubico OTP, OATH-TOTP, OATH-HOTP, Smart card (PIV) and OpenPGP.
Typically FIDO2/WebAuthn is sufficient for most users and should cover 99% of regular authentication cases. It should be completely sufficient for your use case of BitWarden second factor for login/authentcation.