Usability is the entire focus of what they are doing. They aim to make it possible for non-programmers/non-sysadmins/non-security geeks to set up their own whistleblowing framework. Think journalists, volunteer orgs, activists, dissenters...
I think the word here is accessibility, not usability. Every step of the process can be made usable without the need for JavaScript.
From a security stand-point, I don't trust whatever JavaScript engine is running, even more when considering non tech-savvy people.
An activist could find himself in a delicate position and discover that many CPU cycles ate away whatever battery was left in their mobile devices, just to display three Canvas elements in a row, with the text "Tulip", "not", "found" in a cool font.
Now the browser can crash due to a flaky HTML5 Canvas implementation in addition to the JS engine.
