How does this tennis ball thrower for dogs work?

I understand why a long augmentative arm extension could help to throw a ball (it’s leverage right?). But why does the flex in the plastic help? It seems that it springs a bit and that somehow helps to launch the ball farther. Why is that? It seems like a stiff extension ought to conserve all the energy from your arm better. Anyone understand the physics here? http://www.slatergartrellsports.com.au/media/catalog/product/cache/1/image/9df78eab33525d08d6e5fb8d27136e95/w/o/woomera_tennis_ball_throwers.jpg