Duo works just fine on the cell phone and the ability to get codes when not connected to any network is a killer feature, but the Apple watch is where Duo really shines. I can respond to Duo push verification on the watch even without the watch app installed or with the watch app installed I can use the watch as a token and get code that work instantly. This makes 2 factor even easier than before.
ProfessorChandler about Duo Mobile