I actually think Slack doesn't bridge very well with Matrix. One of the things I'm having issues with is the threaded chat, where in Matrix every thread appears as individual message replies, leading to a very confusing overview if multiple threads are being replied to at the same time.

Also, the API token is hard to get and it says you might get banned for using the 'xoxo-' token. Though I did it anyway :)

I was a big fan of Slack until they dropped their IRC bridges, but unfortunately some communities I'm on are still only on there.