I have a herniated disc in my neck, and I was waking up every morning with a lot of discomfort. I tried several different pillows and I purchased this one because the others weren't giving me any relief. Even stretching my neck muscles every morning for 15 minutes didn't completely eliminate the pain. 
It took a few nights to get used to it, but by the second morning I noticed a difference. It has been almost a month and I'm amazed at how much better I feel upon waking.  Although the website says you can use the pillow to sleep on your side or on your back, I don't find it comfortable for sleeping on my side.
I chose the medium sized pillow, which seems to be the right size for me.
Purchasing this pillow was a great decision. I highly recommend this product.