Bought 2 of these fans. Excellent value. Excellent design.
They are extremely quiet, inaudible in low RPM base mode, and still very quiet at high RPM. Even low speed shifts considerable amounts of air, and high RPM shifts huge amounts, reducing time required in this mode.
Much of this extra quieting comes from the mechanical isolation of the suspension rubber mountings.
(Note that the design only allows one-sided mounting, so if mounted for example in a case will only work as an EXTRACTION fan).