FlipBook has a more natural look and feel to the drawing. And it automatically stores the ink on top of the paint to make your scenes look better. This makes the compositing look better. It has painting features that no other app has to make your painting faster and easier. And above all it is the only app that lets you fix your timing while the scene is playing. Every other app makes you stop playback, find the frame to change, open a dialog, make the change and then play it again to see how it looks. FlipBook lets you do ALL of the without stopping the playback. That means you can see the change immediately. It saves you time and effort. So you can get better results with less effort.
This feature alone should be all the resason you need to use FlipBook. Even if you only use it to learn or fix your timing.