When federation works it is good. The instance I signed up for was missing quite a bit of posts across many of the different communities I had signed for. It seems better now after a recent upgrade, but unless one checks manually there is no way to know for sure if one’s instance is federating properly.

The other issue I find is that because anyone can create a topic on any instance, that can cause fragmentation of less popular topics so basically none of the instances has a good representation on that given topic because the few people interested in the topic are scattered.