It ignores all NSFW communities. I'm planning on adding a switch for that, but if you really want, you can change nsfwFilter property in local storage through devtools. all is for everything, none is for no NSFW and only is for only NSFW communities.
Sometimes it fails to follow a community. Maybe it's because community is not yet "synced" to the instance you logged in from. Don't know much about exact reason, because I'm new to lemmy from the tech side.
There is also a planned feature to exclude whole instances. Currently only possible with editing local storage.
This is really nice; I second another person's opinion that it resembles a stumbleupon just for lemmy. Some kind of "Not Interested" button would be a good idea, though I don't know how feasible that is.
At any rate, it's a really cool tool, and I appreciate your having made it. I'm excited to see if/how it develops.