Have you tried it on your pump?
Yes, I have the dimmer plugged into the DC jack of the controller, and the power supply plugged into the dimmer.
The modulator/dimmer has an "off" setting that the knob clicks when it turns off. The dimmer is supposed to gradually change the power from 0% to 100%, which it would seem to do.
The controller, it seems, needs at least ~50% power to be turned on. So, on the dimmer, you have to turn the knob some distance past the "off" position in order to reach the power level where the controller turns on.
The dimmer works. When I turn the knob down I can feel that the strength of the pump decreases in all modes.
However, the minimum strength is still too strong for my personal tank; it still blew everything around more than I hoped (although it didn't rip my elegance out of the sand immediately).