My use of a booster is as a Volume boost (mostly get's switched on Live or for solos during jam sessions). At home I lower the Vol knob drastically to use it as an EQ of sorts.
The Retro-Sonic is in effect, a BOSS FET FA-1 Amplifier clone, with modern modifications (footswitch, true bypass). With the bass and treble knob at noon, you get a PURE clean boost that doesn NOT touch your EQ. With your treble higher, you get GLASSY tones, and adds chime. I was so surprised I could get my clean Vox tone when I'm not at home.
There's also a toggle for a bass cut so you can get faux-Rangemaster tones although it is not in anyway one. So don't expect for a RM setting to sound like a real RM when stacked with a Fuzz Face behind (ala Sunface). Also inside are 2 toggles to make the Boost into more of an OD and another to lessen the treble range, that way you can make minute changes in the upper frequencies using the knob.
All in all it is a boost pedal, and there is plenty of volume on tap that it borders on the ridiculous. Let's just say unity is like placing the knob at '1', AKA 7 o'clock.