Here's my experience. I have three devices I use to connect to my XMPP server: phone (Conversations), PC and laptop (both gajim). Each one generates a keypair. I verified the public keys of PC and laptop by scanning a QR code using Conversations (phone). Conversations remembers all fingerprints as my own. Next time I meet a friend, they scan the QR code on my phone. They now have verified all three of my devices.
Here's my experience. I have three devices I use to connect to my XMPP server: phone (Conversations), PC and laptop (both gajim). Each one generates a keypair. I verified the public keys of PC and laptop by scanning a QR code using Conversations (phone). Conversations remembers all fingerprints as my own. Next time I meet a friend, they scan the QR code on my phone. They now have verified all three of my devices.