The concern I have with these federated instances is I don't see how they resolve the long term problems of stability.
Content on instances can disappear at a moment's notice if it goes down. My favorite part about reddit is the amount of information it has that is well-indexed by google.
These Lemmy and kbin alternatives might fulfill the moment-to-moment chatter, but it worries me that there's no guarantee of continuity for information. The best you can do is be discerning about the instance you pick. If there was a mechanism for distributing information across instances so it's saved, or some other assurance it'd make me happier about it.