From the builders of the first open-source FIDO2 security key:

Secure Firmware

SoloKeys with “Secure Firmware” come with signed firmware and are ready to use right out of the box. The protected bootloader only accepts updates signed by SoloKeys, ensuring the security of the stored key material. Custom firmware cannot be installed.
Scroll further down if you’re interested in the “Hacker” version with an unprotected bootloader.

Accessoires

Lanycard and colorful silicone cases

Hacker Firmware

For developers, there’s the “Hacker Firmware” version with an unprotected bootloader,