Does the tool allow you to drag in multiple images to make one big tilesheet with them all in it?
Considering the program gives more control over the sprites than most sprite packers, adding the ability to pack multiple images would automatically make your program better than almost every sprite packing tool there is (including ones that range from $15 to $70, no joke). Sprite packers that actually allow control over images are weirdly rare and I don't know why.