The Hammer Strength unilateral supinated-grip pulldown is one of my favorite machines. It's nearly impossible to duplicate with free weights what this machine can do.
Several training methods work great on this machine, like maximum tension alternating pulls (hold one side isometrically in the contracted position at the bottom while the other side is moving). It also works great with bands for added accommodating resistance.
Coach Boyle's been dragging his calloused butt through the weighlifting business for 25 years. During that time he's made a few mistakes, but luckily for you whippersnappers, he wants to save you from making those same mistakes.