Finally an argument that is concrete and understandable! Seriously, this is the first comment I've read that is tangible as opposed to theoretical. All the other complaints are on the basis of being morally offended by the ratio of resource usage vs. application functionality.

The nice thing about slack is that it will run about anywhere. The app on my phone magically knows if the app is not running on my laptop and will then and only then send me notifications. But, I'm not suggesting this as a solution for you -- best productivity killer I know is having to pay attention to yet another device while trying to get work done.

Depends on your environment, but I have of one very effective and successful coworker who just flat out refuses to use Slack. The number of companies where that is acceptable is probably limited. Unfortunately.