Extremely quiet and well designed fans that are absolutely amazing at their job. Since I live in a dorm where I can't control the heating/cooling, the sound of the fans is usually overrun by the loud A/C unit in my apartment. However, even when the A/C is off, I barely hear a thing. These fans truly live up to their reputation of silence.
Quiet, and belt quite a good amount of air. Great for case/rad fans. Bit on the expensive side but they're black and the quality shows when you take them out of the box. Mounting is a breeze in either format as well.
Picked up a couple of these fans on a friend's recommendation since the fans that came included with the Fractal case I bought aren't PWM. Solid construction and whisper quiet.