If the picture and model name haven't given it away, the Antec Kuhler 620 is essentially a cut down version of the 920. They use the same mounts, have the same form factor and aesthetics, and function similarly. What separates the two, apart from price, is the significantly thinner radiator and inclusion of a single one-speed fan. With no PWM control, there's no need for the USB header connector nor extra software.
So how does the lesser 620 perform? With the 2600K set to 3.7GHz the mean reported temperature across all four cores was 49c, and at 5GHz, a toasty but tolerable 81c. Essentially the 620 sits somewhere between the quiet and extreme settings of it's bigger brother, while maintaining silent operation.
When compared to our reference NH-D14, the 620 falls short by a couple of degrees, but can be found for a few bucks cheaper. It's slightly louder too (you can hear the water flowing through the head unit), but most cases should muffle the sound completely. For the asking price, the Kuhler 620 is quite an attractive piece of kit, especially if you're trying to maintain a compact system where bulky air coolers are problematic.