I also think that the marketing is pitched too heavily towards what Slack is, and what this product isn't. It's target towards someone who hates Slack rather than someone who wants the product for what it is, but most people who hate Slack are probably using it because their org says so, and their org doesn't think it sucks (because it has stuff like compliance and auditing and other legal what-have-yous).
Maybe I'd use it for some low-key personal thing, or maybe I'd just host an IRC server for the hell of it, but if I was running a startup I'd hold off on signing up until it matured a bit.