Cooling Gel Mat for mattress?

Has anyone tried one of these things and if so, what do you think of it? I'm referring to the Forever Cool one from Walgreens, Cool Gel Solutions one or the Cool Sensations one. There was an article in Men's Health for the Cool Gel Solutions one. Kinda pricey, but if worth it, I'll buy. Tired of sleepless nights due to being hot.