After playing for a long time with the official Sony Dual Shock 3 pad I often find my hands hot, sweaty and cramped... With the ChillStream, the cool air blowing is enough to keep your hands from becoming sweaty and the shape combined with the massaging flow of air is enough to keep my hands getting cramped regardless of how long I spend playing.
Though as pointed out before, there is no PS button (which is a MAJOR design flaw) and the L2 & R2 triggers are replaced with buttons, making the controller useless for Racing games but doesn't matter for games that don't require pressure sensitive triggers.
On a plus side there is the D-Mode, which switches the 8 Direction D-Pad with the Analogue stick meaning that PSN and PSone titles can be played as you prefer them (which can help a lot of you like playing the PSOne games).
Basically it's missing a few important features. It is nice and relaxing, is a cheap additional controller and it works fine for a lot of things, but is totally useless for others.
I'de say unless you know you can put up with it's missing Triggers and PS Button, give it a miss and go official.