To get something like this coded manually in OpenGL would take me at least 3 weeks, I'd estimate. With Quartz Composer it wasn't much more then a few hours. With QC you can do a whole lot of interesting things very, very quickly. Also at first the program may appear to be not much more than a demo maker, I think it can become quite a bit more over time.
Programming QC feels more like hardware design than actual programming. I think it could be a good teaching tool for programming intro courses. Forget Logo and the Turtle and give the kids some of this stuff to play around with.