I was expecting a lot when they announced video-conferencing, given that the app itself is well-designed and performs generally great. But when I finally got to try it it crashed the app, and never really worked ever since.
Such a shame, I'd love to have a single app for messaging and audio/video chats.
I wish that the slack company would focus on performance and e.g. making video calls work on Firefox.
As alternative recommendation, matrix.org is somewhere between IRC and slack/telegram. It's an open protocol like IRC, so you can pick your preferred client (and server) and aren't trapped on some platform. Open source also means that it's not as UX streamlined as proprietary stuff, mind that.
It does have a lot of modern features like attachments, reactions, replies, etc., which I found to be almost unusable on older systems like jabber.
Such a shame, I'd love to have a single app for messaging and audio/video chats.