At my company we use it and there's a timeline to shut down Skype for Business in favour of it.
The app is incredibly slow, doesn't have tabs so if you're in a chat, then you want to reference a file you're making in the tools you have to click out of it.
Teams chats and 1 on 1 chats are another "web page" to load.
Clicks load as fast as my 1mbps internet connection in 2004
Skype for Business is still used for chat even though we're told by IT to transition because the app is so slow.
I just see it as crap clone that Microsoft coded together in a messy hurry to copy Slack, and then included it free in their Office subscriptions.
The conversations around using slack are that it's really expensive in comparison to free.
Why isn't that anticompetitive?