There’s no open source websockets-based ES publish api, you have to use the closed source private service made by the company which created this project.
Sometimes you want to access the application from outside, available via some corporate proxy, and all do not support WebSockets, and even those that do on paper are so complicated to set up that some admins abandon the idea (looking at you MS Forefront TMG). So it's good to know that you'll get the baseline functions working without WS.