Pros: Feels good to sleep on a cool pillow. It stays cool but not all night.
Cons: The leaks will wake you up very rudely in the middle of the night.
When I first got a Chillow, and when I bought the second one, it worked fine. Eventually, your head and neck warm up the water and it loses its cool. But when you roll over, the new contact area is cool. But after a few months the plastic cracks, and not just at the seams. That will wake you from a sound sleep, with you, your PJ's and your bedding wet with cold (room temperature) water. So I purchased a pool and toy repait kit. It never leaked in the same place after a repair. But once the plastic starts to crack, it happens more and more often, maybe every couple of months. After a year of fixing leaks, I bought a second one, hoping that the manufacturer had changed the plastic formulation or used a thicker, less crack-prone kind of plastic. No such luck. After a few months, it too started to leak. When they introduce one that lasts two years or more without leaking, I'll give it a better rating.
A second flaw is that over time the internal sponge-like pad can move and fold over on itself. The only access is through the fill port which is about a half inch in diameter. You have to drain all the water and fiddle around with the pad to get it back into place. Then you have to refill the whole thing again, removing as much of the air inside that you can. It's a clumsy process.