I tried using Zulip for a short period of time at a small company with lots of chat and was completely overwhelmed by the volume of messages that that I had alerts for. There didn't seem to be any obvious way to choose not to include the whole company in a conversation by default, allowing them instead to opt in. I had thousands of unread messages and just declared bankruptcy by deciding not to read all of them. I mostly had to just wait for someone to @mention me.