Marques Brownlee thinks the lack of Face ID will be the biggest gripe. I agree. And I love his central framing for the review: that the Duo is extremely polished around the edges (figuratively, but also true literally) but rough in the middle.
But he spends more time griping about third-party apps that haven’t been optimized for the Duo than most other reviews, because he oddly seems to personally rely on a lot of apps from shitty iOS developers, like Discord and Google Calendar. I get it, Google Calendar is very popular. So too is Discord — it’s #6 in the App Store today for the “social networking” category. And I get it, Brownlee splits his time across iOS and Android. But Google is a notoriously terrible iOS developer. Every time there’s a major hardware display transition on iPhones that requires developer support, most of Google’s apps are late. And whatever the reasons for Discord’s popularity, it’s sure as shit not the quality of its app.
The best apps for the Duo are the best apps for iOS generally: ones that are exclusively for iOS. (And Brownlee sings the praises of several of them, too, like Carrot Weather.)