Great introduction to the basics of image editing, has some issues
Sumopaint is great as an alternative to GIMP or photoshop style programs. It does have three main issues. The first is that it often thinks you have an area selected even when you don't and as such won't let you draw or edit outside of the supposed selection, we fix this by selecting the lasso tool and clicking anywhere in the image to de-select. Second the saving process is somewhat tricky, our computers do not recognize a .sumo extension as valid so it often gets deleted when students are titling work, and then wont open next class as it has no extension. Last is more a student issue than a sumopaint issue, students love the symetry tool and if not watched can really lose a lot of time with it, and overuse it as a tool. extra issue, it is not possible to edit text once you have left that specific text box.
How I Use It
I use Sumopaint in my games lab class where student groups use it to draw game boards to use with their 3D printed game pieces. I also use it as a tool to create logos, and diagrams with other classes. We have used it to "Photoshop" different images as one off activities with various groups.