Don't purchase this product the differences between sizes is so great they wont fit and they will not refund your money I binned mine after spending $70 dollars for something I cannot use.

Great for cardio workouts. Without it, after a couple of sessions of cardio on a threadmill, my knees tend to ache in the wrong places, like on both sides of the knee cap and sometimes on the bottom of the start of my thighs. Using it helps a great deal in minimising the ache.
Provides good support and stability for my knees when I am on the treadmill.
It does get sweaty and I don't think I can wash it. At least, I don't want to risk it. Takes a while to get used to. Gets loose over time and doesn't grip that well anymore.