We've been using it successfully for a long time too. Real nice bunch of fellas. They did remove mobile notifications without a subscription recently and the price is quite high ONLY for notifications. I do not fault them for doing it but it made recommending them a tiny bit more difficult. The other major issues IMO are the super basic mobile client and lack of any kind of native voice/video chat. You get a button that provides a link to a chat service of your choice. For example you pick a Jitsi Meet instance and Zulip gives you button to create and share the url easily. That's it. I wish there were something a little better integrated.