Beeper is supposed to be a "universal messenger" that acts as a central place for all your messaging apps. I originally signed up because I wanted to be able to iMessage on my Android device, which has worked relatively well. In order to use the app's SMS bridge though, you have to set the app as your default SMS app (an Android requirement, no getting around it.) Unfortunately, it's just really difficult to compete with the system-level messenger app.
I've been chatting back and forth with them, and their support team has been pretty responsive, but I'll likely stop using it soon. Their app is just too buggy to be such an important part of my workflow as a default SMS app. No RCS support, notification issues, totally missing SMS messages entirely with no way to recover them? (Rare, but destructive.)
Love the idea, but needs a good bit more work. (Sorry to the team, I know some of them are here on HN.)