I remember seeing that a couple of years ago, but bought a small one surplus under $40 (American Science & Surplus), they had theirs on sale at the time. Last weekend I through together a fog/fountain thing from an old humidifier guts. Guessing it's surface area. The cleaner vibrates the stainless pan, where the fog comes off the humidifer transducer directly.
I just wanted the fog, the foutain part splashes the sides of the big plastic dome I used. I tried putting something just above the transducer to stop the foutain effect, but it also stop the fog. Also, increasing the water level had little to no effect on the fountain, but did reduce the amount of fog. Believe the fog forms as it erupts from the surface of the water.
I seldom use chemicals in my cleaner, but don't do anything major in it anyway.