It's nothing that exotic. I use it as MFA for a few different accounts as I assume anyone who has one does. :)
Using one easy example, I have myname@anemailprovideryouveheardof.com set up and I can clearly see "myname@anemailprovideryouveheardof.com" as a linked account on my yubikey on any device. I can't do anything with it, but I see my username in the format shown above, and the one time code counting down.
I don't actually know why I haven't gone to their support - hadn't thought about it for awhile until reading this thread, so that's a good suggestion and will do.