You can compare the controller a little bit to a pencil. Drawing with a pencil is way easier, faster and nicer than with a mouse.
In resolve you'll find yourself using the primary controls a lot, let's say 75% of the time youre workíng in there. Specifically these controls are very hard to use with a mouse and very easy with the trackballs.
My last point is that you can keep your eyes on the image while you're using the controller, which makes the whole process more 'organic' as you work with your hands to craft what you see.
I have a tangent wave panel and i absolutely love it. Its mobile and has usb connection and also text labelled leds (something the artist color is missing) so its easy to learn.