I was going to install a similar PWM speed controller on a Heng's fan, but discovered (a) it made an loud high-pitched noise whenever the fan was set to any speed other than full, and (b) it drew several milliamps of parasitic current while turned off.
Maybe this controller is better, but those are a couple of things to maybe test before cutting and drilling.
I did install the speed controller on my stove vent and it works great. I installed it down-stream of the existing switch to avoid parasitic current draw.