We use it at our small (15 person) startup. I like that topics are light weight, like git branches, but despite that we struggle to use them effectively (generally dumping thoughts in a select few topics)

One major quirk of the interface is that can be difficult to, at a glance, identify what topic/dm you are actively on, which has lead to a handful of "Oops, what was supposed to be a DM" message deletes.