I don't know the security ramifications to what they've done, but as a user, I find Blizzard's current implementation to be the golden standard that everyone else's implementation leaves me feeling bummed by.

I login, I get the "hey, we just sent the code VH3Z (making it up) to your phone/watch/whatever" and then on both my phone and Apple Watch, I get a prompt saying the Authenticator has that code and do I approve or reject. I tap approve on either device and then the current window I'm in within whatever Blizzard app (whether web or Battle.NET) switches to the actual content.

So long as the phone or watch are present and charged, this is such an easy experience.