Sounds promising. But not sure what this adds on top of Hangouts, which has a great group (and of course one to one) video calling feature. The only difference seems that Duo works with phone numbers, not Google Accounts.
Hangouts works on phones, tablets and laptops. It does voice, video and text. Fragmenting these features across apps and devices seems to be a major step backwards...but apparently two apps is simpler than one?
Instagram and Whatsapp are just examples of how not to kill a successful product. Turns out it's quite simple: You change nothing.
For a long time it seemed like the strategy was to change nothing. Now it's become clear the strategy is to be scared of changing anything, just leave it to fester and fall behind then panic and recklessly start cloning competitors features and diluting what made the service compelling in the first place.
Which is a huuuuuge difference. This is the same factor that made whatsapp so popular on the smartphone compared to all other other chat apps that were popular at the time (including google talk) but where each system was using a different account creation/login flow on that tiny screen, Whatsapp came along and had the brilliant insight/accident of simply supporting your phone's addressbook to find you and your friends. Even facebook chat couldn't keep up with them even though facebook app was installed pretty much on every internet connected phone at the time. Rest is history.
Perhaps as a video-calling alternative to Whatsapp? (given that neither of them are open source)