Just tested it, it works pretty well. Really simple to use. The only thing I noticed is that it clips below my taskbar and I couldn't figure out a way to resize it, since it's a borderless window. KDE rules took care of that by manually setting it to 1920x1066 resolution.
Not sure if drag-and-drop is supposed to work on windows, but it doesn't on Linux. It would be nice to have as a convenience feature.
Also a customizeable "size" of the inner edges would be a useful feature as well. Currently I assume you just make one step on the edge and another if "inner edges" is checked, which means the normal will always be 1 or 2 pixels thick, but some larger sprites might need more than that, so a customizeable number of steps would be awesome for future updates.
Thanks for the nifty tool :)