Saw this on SlickDeals a few hours ago but already expired and back to normal price US$40. Then I checked again a few minutes ago and it's back at 50% off for US$20.
I don't even have a prime membership and bought 2 for AUD$61.72 delivered. Great deal considering the normal price is US$40 each!
Yubikey 4 Nano here:
https://www.amazon.com/Yubico-Y-159-YubiKey-4-Nano/dp/B018Y1…
Check the comparison here:
I got one of these years ago. The original yubi key… and I can't work out how to get the thing working… :D they sound like a really good and handy tool to use. I guess I'm just to dumb to work it out…