Pros: Initially very cool and comfortable.
Cons: Gets too hot; wrinkles, bunches, and moves around; leak potential
I had a problem with the chillow that I did not see mentioned yet; but pertains to the basic function of a chillow.
In my use I found the chillow to initially be all that it was advertised - cool and comfortable, it definitely helped me get to sleep. My problem came later. Apparently after my head was in contact with the chillow for a while, I ended up raising the water temperature to body temperature. The results being I was waking up with a hotter pillow than I started. It helped me get to sleep because it was cool but then it woke me up because it was too hot.
I figured that I started with a cool pillow, ended with a hot pillow it averaged out to not worth the trouble - so I stopped using it.
Other problems were that the chillow moved around inside the pillowcase, often bunching up (wrinkling) or moving away from my head. I also developed a leak after a few months.
It's a great idea but too many flaws.