Delibr loves Slack! We use both Slack and our own tool on a daily basis. In fact, we actually have a Slack integration.
We use Slack to spread information, for quick questions and to notify other team members. However, longer and more complicated discussions are done with Delibr and short meetings.
The main advantage with Delibr is that your discussion will be structured. A team member that joins the discussion at a later stage can quickly get an overview of how the discussion went, without having to read a cluttered chat transcript.
Here is an example of how it looks on a Delibr-connected Slack channel.