I just spent a goodly amount of time testing it out. It really helps on cleaner settings because the Jet City doesn't have a ton of clean headroom. It can almost sound single-coil-like, just without any hum. Before the mod, my neck pickup would get muddy very quickly when you rolled down the volume. The bridge wasn't anywhere near as bad. The middle position rolled off a bit combined with my Chorus Factory gave a pretty convincing fake 12 string.
That naturally made me want to take my fuzz pedal for a spin with it. It really sounded great for Hendrix-y kind of stuff and for Iommi stuff on the bridge pickup. I found myself rolling off the tone knob a bit because my Cool Cat Fuzz can go from fuzz to fizz awfully quickly. Nevertheless, rolling off the volume made for more single-coil-esque output which I think plays better with fuzz pedals.
Then I cranked the gain and was going to try rolling off the volume there. I got too caught up playing 80s metal riffs so I'll have to try that more later. What little I did test showed that I can roll off the volume and the neck to clean it up a bit and it doesn't descend into mud at all.
Long story short is that it is a cheap way to make better use of my fancy new tube amph. It really widens the sonic palette of my guitar tremendously. For the first time in my life, the knobs on my guitar won't stay parked at 10.