>"They both work as notch filters, correct?"

No. The C-switch just contains a couple of caps, which are placed between the hot output wire and ground (parallel to the pups). It sort of simulates using a cable with higher capacitance. A pickup with a cable attached has a lowpass transfer characteristic, and the cutoff frequency is determined by the inverse of the product of inductance and capacitance.

That's why one can simulate a higher inductance pickup by using those parallel caps. You can increase either L or C, the result will be a lower cutoff frequency.

To be more specific, the lowpass is of second order and has a resonance, which shapes the sound quite a bit. In principle, the resonant frequency is determined by LC, and the height of the peak is determined by the resistances in the circuit (pots, DC resistance of pups).

IMO, the C-switches are very cool, way better than a conventional tone pot. Sorry to hear that Helmuth Lemme didn't respond to your inquiry. Perhaps he doesn't read/understand the english language?

>"Hey Pete -do you mean to say that a Varitone bucks hum on single coil guitars?"

Not really. It is just a wise idea to make any coil in a guitar a humbucking one. BLs Q-filter is, AFAIK, also humbucking. Otherwise, it will pick up hum like any single coil pickup. Another option is to shield the coil.

I don't know how the Gibson units or those on ebay are made, but I think it's safe to assume they are single coils and need extra shielding.

>"The Qfilter is an LCR network too by the way!"

Yes. But the function is determined by the inductance. In a way, the RC network just limits the operating range a bit and evens out the response.
Let the thunder roll and the lightning flash, I'm doing alright for country trash.