A physical authentication device provides an extra layer of security that doesn't come with normal 2nd-factor authentication. SoloKeys sells open-source FIDO2 security keys that work similarly to Yubico's Yubikeys and are quite cheap at $20 - $25 each. Plus, customers can purchase a handful of coloured cases for easily telling them apart. Solos are available in USB A or USB C. NFC versions (Solo Tap) are coming soon and will cost $35 - $40 depending on USB type. These items are useful for protection when logging onto Gmail, Facebook, Twitter, and other sites.