I've actually used hangouts at the previous company (so roughly 2012-2015 or so), and it worked fine I guess. I don't remember what were the reasons not to use it instead of Skype, but I'm sure there were some.

But I guess we don't really need the video calls that much (After all, who'd want to see video of engineers working mostly from home, right?) and the ability to self-host and integrate Mattermost with the issue tracker etc. is quite neat.