The red in front of my '71 JMP, (volume 2-3, barely breaking up but plenty loud), into a 4x12" is a thing of scary beauty.
Gain around 12 gets more out of the switches, which have a huge influence on tightness, overtones and note definition. 1984-era VH, Steve Stevens and Cantrell tones are all there with some tweaking.
But it can also get loose and sludgy with the variac switch, full gain & boost, and the structure switch. Echoes of Entombed, Probot, early Metallica, even Mastodon. With a really clean amp, I think even djenty grind might be possible.
There's always more of an amp feel, rather than just that of a pedal, although more gain tends to sound more compressed. The EQ is very effective and interactive. I barely go over 12 o'clock with the bass, 2 with treble. The mids - like on a good amp - can radically change the basic tone character.
On a side note: before buying, I also tried the Mesa throttle box but found it too limited. OTOH, the Fulltone Secret Freq. was very interesting, but not what I'm looking for at the time.
"Recording exactly what a musician hears turns out to be a really big deal." Bob Olhsson
"Who cares about efficiency, when we're talking about music?" Rupert Neve
"it'll sound different through a microphone, anyway" Keith Carlock
"no room, no boom!" Michael Wagener