The Wall Street Journal reports: [edited]
Duo, which is available for iOS and Android, has a single purpose: one-on-one phone video chats. There are no video filters, no group chats, no texting and no GIFs. Duo’s interface and setup are as bare bones as the app’s purpose. You sign up with just a phone number. On the main screen, there is one option. Tap “video call” to scroll or search your contact list for someone to call. That’s it.
On the most important issue — video quality — Duo performed in line with other chat apps I’ve used. The visuals were sharp over Wi-Fi and blurry over most cellular connections. Google says Duo can switch to an audio-only feed if video quality deteriorates too much, though I never ran into that scenario. Duo’s calls are encrypted end-to-end, as with some other apps.
Duo has one feature called “knock knock” that sets the app apart from its competitors. If someone calls you using Duo, a notification shows you a video preview of the caller before you pick up. Seeing a video stream of your friend waiting for you to pick up is fun, but it wasn’t a compelling enough feature for me to try to convince dozens of people I care about to download another app.
Duo can only be used on phones. I use a tablet daily, and I have laptops for work and personal use. If I want to video chat with a colleague at work or a friend while lounging on my couch with my tablet, Duo isn’t an option. Even if I wanted to convert to Duo exclusively, I’d need to keep around Hangouts and FaceTime (or both).
If you absolutely desire a stripped-down video-chat app, and think you can convince others to download one more messaging app, Duo is good enough for a look. Just don’t expect it to replace your other messaging apps.