When Neephid was doing his Gibson Ripper Rescue, he installed a Varitone on that.
If I can throw in my 2cents here, I own a guitar with a six position Varitone on it. It is an interesting thing; way more so than a straight tone knob. Generally, I'll just leave it #1 position (Open/Bypass), but the other five settings give a tremendous amount of variety. Interestingly, some outboard effects that sound terrible in position #1 sound fantastic in different positions, so it can open up for a bit of experimentation. I love #6...it just squeezes the output and the guitar sounds like shortwave radio. Great for introductions.
P
Position 1: Bypass,
Position 2: 5db at 1950hz,
Position 3: 12db at 1100hz,
Position 4: 16db at 620hz,
Position 5: 18.5db at 360hz,
Position 6: 21db at 120hz.