Placing a properly tuned resonant system in a room can counteract a resonant acoustic energy mode, making the room response flatter and more accurate. That's how Helmholtz cavity resonators and resonant panel bass traps function. But those kinds of devices are built to work at specific frequency ranges with rather narrow bandwidths and only work properly when tailored to suit the specific resonant problem. Measurements are required and well understood acoustic engineering principles apply. Of course no one is even attempting to measure those silly little magic cups or use them in any kind of reputable way, although they could be measured to determine their actual acoustic behavior. Like voltronic notes, those tiny cups will be physically incapable of having any affect below a very high frequency range due to the length of the wavelengths involved.
There are two small helmholtz chamber resonators molded into the plastic intake system of my Mazda which aren't that much larger than that little trophy-cup thing pictured on the dash. Of course they are accurately sized and placed in the intake to counter buzzy acoustic intake resonances (or alternately, the Mazda design engineers may have placed them there to enhance certain cool-sounding 'vroom-vroom' resonances).
Terry, those pine-tree air fresheners make the RepoMan soundtrack sound incredible!
Just ask Miller- "There's one in every car, you'll see"