I've used both. Truthfully, I didnt notice any difference between them. I've got a really good cooling system though, so maybe I would have noticed more of a difference if my cooling system was a little more inadequete.
I've also used both the water wetter and the purple ice and didn't notice a difference. But like KV said, I also have a very good cooling system and didn't notice it cuz of that reason. I know of some others that have used it and had good luck with it.
Their Hypercool product is similar to Water Wetter.
Pretty much exactly the same reduction in coolant
temperature. If you run your engine continuously
above 5000 rpm, for 20 minutes or more, (like you
would during an open track event), this product
tends to produce some froth. That's why I no longer
use it. It does have some anti-corrosion properties
that WW does not have, however.