This plugin does only one thing, but it does so with great gusto. To call it a 'colour box' would be absolutely accurate but strangely under-selling it. It sounds fantastic.
Slightly oily vintage grit WITHOUT, and this is an important rarity, WITHOUT all the treble frequencies smeared or filtered out. A detailed circuit simulation of a hi-quality old pre-amp from the 60s which has a nearly flat frequency response all the way up to 20kHz, but which provides fascinating colour.
In pre-amp mode, when pushed, there is just a hint of peppery bitterness from (i THINK) the crossover distortion.
In high-gain PA mode, the output is routed back to attenuate the push-pull stage, removing the "pepper," thundering up the sound and—when pushed—adding some great, really rattly overdrive, and making basses chug without making them at all muddy.
currently, however, my primary use for it is a bit niche. there are two(!) modeled inputs, a buffered input for microphones and a secondary aux input which was originally for turntables. i'm using the aux-in to punch up the fake record scratches i make with cableguys time-shaper. it makes them sizzle and jump and sound a lot more 'alive' than they do coming straight out of cable-guys itself.