Knee-T DLX Memory Foam Knee Pillow by Knee-T

This product looks really interesting, but - to justify the price - can someone please explain to me how it's better than a nice big, thick pillow?

Does this strap prevent you at all from waking up on your back? I always start on my side and wake up on my back, with my back hurting.

Does this pillow separate the knees as well as the ankles?

Can I buy a pillow case for this pillow?