Glancing at it briefly, I like the Workflows feature. I'm a long time Sidekiq user (Ruby), and while you can construct workflows pretty easily (especially using nested batches and callbacks in the Pro version), there really isn't a dedicated UI for visualizing them.
I’ve been using river for some low volume stuff. I love that I can add a job to the queue in the same db transaction that handle the synchronous changes.
From an end-user perspective, they also have a UI which is nice to have for debugging.