The Antec Kühler H2O 620 seemed to be an excellent watercooling system at first sight. It is easy to install, is elegant, and quiet; and it cooled our CPU reasonably well. However, the problem is that you don’t buy a watercooler system to cool your processor "reasonably well". When you buy a watercooler, you are looking for some extra cooling, and this product doesn’t provide it.
So, if you are looking for a watercooler just to know your computer isn’t an ordinary air-cooled one, you can buy the Antec Kühler H2O 620; it is a good product that will not give you headaches. But if you are looking for a good cost/benefit ratio, just forget about it and look for a good air cooler.