However if all you want is a low bandwidth text only slack alternative to use with slow and glitchy cellular I’ve got an excellent alternative:
wee-slack + mosh
https://github.com/wee-slack/wee-slack
wee-slack gives you a minimal terminal based slack client within weechat and mosh handles ssh connections over low bandwidth, high latency connections.
Using this set up I’ve been able to reply to messages at times a ping to 8.8.8.8 resulted in >90% package loss.