The PlayStation 3 controller is a starved, emaciated excuse of a video game controller. It's terribly skinny with no curves and feels like you're holding the result of a skinny TV remote's incestual relationship. The Xbox 360 controller? Now there's something worth holding. And with this Cronus adaptor, you can use the Xbox controller with your PS3.
Or you can use the PS3 controller with your Xbox 360, but why oh why would you want to do that? Oh yeah, the d-pad on the Xbox 360 controller is awful. Maybe you've grown really comfortable with the crappy PS3 controller -- people often have irrational personal tastes for these type of things. Cronus works every which way. Play with whichever controller you're comfortable with by plugging in the Cronus dongle to the console's USB port and sync your preferred wireless controller to the adaptor. It's supposed to be pretty simple.