In the last couple of versions I didn't test the droplet because I'm working on a cross-platform GUI. I'll do some testing tomorrow, if you are in a hurry you can fire up the Terminal and install Pillow (pip install Pillow), and then call
python ./kcc/comic2ebook.py -p K4 filename.cbr
assuming you have all the stuff in the REQUIREMENTS section of the README.
Let me know if you need further help!