One of them is a black one that work gave me for use with the work computer. I’ve had this Yubikey for over 1 year.
Three of them are blue ones I bought from Amazon, that I also added to my SSO profile at work. I’ve had these Yubikeys for several months.
One of them I keep in my wallet most of the time. One of them I keep on my desk and bring in my backpack when I go somewhere. One I keep in a box. One is somewhere in the room.
I rotate between these, and I switch which one I keep in the wallet, which one I keep in a box etc.
It’s worked well for me so far. None of them have failed yet, and when one does fail or get lost I will remain confident that the other ones I have will continue to work long enough that I can order even more Yubikeys to replace which ever ones went bad.