I use a Yubikey 4 with the GnuPG smartcard applet to secure all my password, sign my emails and connect to remote computers with SSH. It's super convenient and I'd never go back.

That being said I got a bit concerned about the use of closed source components in newer yubikeys (I believe that the yubikey 4 is open source and the later ones aren't, but don't trust me on that).

For this reason I also bought a nitrokey as a backup. It's a bit slower than the yubikey (I use 4096bit keys) but it works well. I really don't like the plastic cap on the nitrokey though, I feel like I'd lose it within a week if I started using it as my main key. The Yubikey doesn't have any protection at all but it looks sturdy enough that it doesn't really matter. It's been on my keyring for months and it seems to handle the abuse just fine.

To be honest, Yubikey was never really open source. Sure, they open sourced _some_ compomnents before but you coulnd't do anything with the source.

Had one, loved it, then lost it, then hated it.

that's why you always have to have two, preferably 3 - one stored off site somewhere. physical locks also come with at least 3 keys.