The Yubikey documentation recommends always buying them at least in pairs. And configure them both for access.
If you use either a Static Password an HMAC-SHA1 Challenge-Response or TOTP with the key you can easily backup the secret material used to program the key and replace the key if one fails.
If you use either a Static Password an HMAC-SHA1 Challenge-Response or TOTP with the key you can easily backup the secret material used to program the key and replace the key if one fails.
Store backups safely.