Seems that, unlike Sidekiq, this starts as a heavily commercial solution, and it shows. Landing page has a pretty big "Buy Pro" call-to-action button. Features like support for notifying slack/etc I'd expect to be present in a free version. Open source feels more of an afterthought. I don't feel comfortable using even the free version, simply because if the project fails financially, it is likely to be dropped altoge…
The OSS product is targeted to small teams, individuals and hobbyists. Pro was designed to target larger teams and the features they would need.