The GuitarSystems 'Junior' range comprises smaller, less fully featured versions of the Dutch company's 'Standard' pedals, which can be adjusted for use in setups with active input signals, such as guitars with EMG pickups.
The TrebleTool Junior is a single Germanium transistor-based treble boost in the style of the classic Dallas Rangemaster, designed to add edge to dark-sounding British amps in the 1960s and used by Brian May, Rory Gallagher and Tony Iommi.
Three knobs control the action - you can turn up the gain, adjust the treble with the tone knob and alter the signal's low-frequency content with the TMF (Treble Mid Full) knob, common to all of the firm's Junior range pedals. Fully clockwise, you get the full frequency range, and winding it back reduces bass - useful for dialling in the amount of low-end for specific guitars.
The TrebleTool will kick your amp up a gear, but it's more of a specialised tool than a general booster.