Yubikey vs. Open-source

Hello,

  1. What do you think about this information that Yubico has replaced all open-source components with proprietary closed-source code in Yubikey 4s:
    https://plus.google.com/+KonstantinRyabitsev/posts/4a7RNxtt7vy

or:

  1. What do you think about using: https://www.nitrokey.com/

Nitrokey is the other one that I recommend on the course.

Its not good news that yubikey is going in this direction but may not be an issue if your need is only a moderate one, and want to add an extra factor against standard threats.