This is an excellent tool. There is 2 problems, when you double tap on the same place it sometimes creates a dot not a line, and well it can't be erased. The other one is at the sliders there is supposedly text to say what the slider does, but it's color is black and the background is black so you can't see the text.
Some suggestions to enhance the experience is to make more grid options for the line setter. And definitely add curves, curves is a must have especially if people want to create a script and use this tool.