I've been forced to use it. It's Facebook, for work (it used to be literally branded with that name). Easily the worst productivity tool I've ever used.

They haven't adjusted any of the engagement levers for the workplace tool, so you get so many notifications that they become useless (and the email versions are just teasers to get you to open workplace), you get an out of order "news feed", the groups UI is hard to understand and difficult to search, messenger is enabled in the UI and you can't turn it off, etc.

But yeah, it's Facebook, and it's what they use for everything internally.