Same as switching pickup response curves. If I could only have one pedal, it would be that. That is guaranteed to provide impressive tone. Since this curve is usually broad and smooth, not jagged and detailed, a parametric EQ is especially appropriate here. That implies rack unit, since no param eq pedals exist.
Research is below.
The guy says nothing about the amp, but rather, general gear principles. The other controls the amount of cut or boost. I'd say this is pretty much the only product out there in stomp-box format to get. It can instantly turn your passive bass into an active. I'll also be using this as a preamp for our cello player for a while.