Of the two communication apps that Google announced last year at I/O, it's not a surprise that Duo found a larger appeal and better reception than Allo. It wasn't battling against existing juggernaut standards like SMS or widespread opponents like WhatsApp and Facebook Messenger, and even at launch, it seemed like it did the basics right. The outcry over its missing features was far less brutal than Allo's and with just a few small changes from Skype and Facetime, Duo managed to delight and impress. Simplicity and immediacy are the reasons I, and many others, fell in love with it.
Over the months, Duo has continued its faster progression compared to Allo. It has kept better rankings overall, higher rating scores, more user ratings, and higher download numbers than its sibling. Sure, it was released earlier, but it hasn't lost that advantage with time. And now Duo is crossing another threshold: 50 million downloads on the Play Store.
That doesn't mean there are 50M active users, but it does show that the app is making its way to more and more users, either by word of mouth or Play Store discoverability. The recent addition of voice-only calls should even make it more approachable and improve usability.