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.
Those guys who think planks and Bosu Ball triceps kickbacks are giving their core a good workout are poor, pathetic slobs. If you really want to work the core, you've got to raise the weight over your head.