I used this to manually control a PCIe slot blower that I had to add to a cheap Dell PC to compensate for garbage thermal performance in the chassis. Worked like a charm, exactly as intended. I manually dialed in the voltage until I got it just at or below the typical noise level of the PC. Now the blower is providing some extra ventilation to clear out a hot spot without adding to audible noise.
Also, the staff at Coolerguys are fantastic.