The tool itself is very convenient.
Many comments make the code easy to read.
Can also be used as a good tutorial for : GUI, Classes, imroi
I myself was in need of a more versatile tool. For exemple being able to save not only the binary mask but also the imroi shapes themself.
With such a funcionality you can reuse the shapes on another image and modify it if needed.
I implemented this funcionality in an enhanced version of your tool. I may submit it soon