Ah thanks, sorry - I don't use either of those, but notifications work just fine for me with Slack, Hangouts, normal messages and all. You can customise notifications and where they may appear on a per application basis.

Mine's on Android 7.0. Samsung aren't too keen on pushing out updates in Australia in a rush; the telcos (Telstra) take their own sweet time too. That's where Apple has them soundly beat. Although, having said that, given last year's update history, perhaps Samsung's model is better after all - I rarely get breaking changes pushed down.