When comparing Facebook Messenger vs Riot, the Slant community recommends Riot for most people. In the question“What are the best Skype alternatives?” Riot is ranked 5th while Facebook Messenger is ranked 33rd.
Ranked in these QuestionsQuestion Ranking
Pro Chat head for quick access
Only for android platform though!
Pro Uses Matrix, the open communications protocol
Pro Supports text, voice, video
Integrates with Jitsi for multi-party video chats
Pro Web and mobile (iOS, Android) versions available
Pro Bridges to other networks
You're not confined within Riot's or even Matrix garden, and you don't have to make users of other networks switch to Matrix.
Pro Widgets support
Want to watch that flick at YouTube and discuss it at the same time? Have Grafana graphs stacked above your DevOps team chat? Collaboratively edit Google Docs and chat over without switching applications? This is possible with Riot.
Pro Very good and simple interface
Riot has a very simple interface, adding the ability for more unexperienced PC-Users to use it.
Con Cluttered user interface
Messenger has so many features accessible from one page that it is often difficult to find what you're looking for.
Con Not very customizable
With so many features in one app, it's very possible you might not be a fan of at least one of them. Too bad you can't disable anything in settings.
Con End-to-end encryption only in "Secret" conversations
If you want e2e encryption, you need to start a secret conversation.
Con Closed Source
Con Owned by Facebook
Con Still in active yet early development
There is clearly a User Experience issue esp. in web version which the developers are aware of and are working hard to improve. They've got the concept concrete, so UX won't be an issue in no time. Most often used parts are functional, but some are yet not.
The success of riot depends on how fast the development is, or it'll get outdated too quickly as developers of Signal and Telegram have predicted.