Thanks for asking this!
The main difference is that, it provides ability to structure the arrows(and hence layout of the diagram) with just single characters as per direction required. In other tools either the arrow direction(and hence layout) is auto-decided by tool, or difficult to change as you want(atleast thats my understanding, please let me know if its wrong). Also, this tool is not as extensive in current form when compared to others.
Examples might help clarify the point : https://blockdiagram.herokuapp.com/examples