Facebook's strategy to create separate apps is a good one, but Rooms seem rather niche. Facebook groups are better for many purposes since they have access to notifications and the newsfeed. Reddit probably works better for large groups and allows anonymity too (though not on a per Reddit basis). So Rooms work for groups where anonymity is valuable (ie. sharing secrets, controversial opinions, ect) and where the groups aren't too large. Here, the discovery mechanism being overly complex actually does provide an advantage. It makes it more likely to be "underground" and hence cool.
I disagree - Rooms seems like it is trying to do too many things at once.
The discovery mechanism is QR codes, which wasn't "underground" enough to boost any marketing or advertising activities that were based on them. In fact, because each room's value relies on user-generated content, I have a feeling that this will be short lived, if only because it is so difficult to get more users into a room to generate content.
One of the reasons subreddits achieved such popularity was because of the extreme ease by which users can find, join, and start submitting.
Without clear connections between rooms, all it's going to take is joining a few empty rooms before users become disengaged and start ignoring invites like they do most other QR codes.
