From Mad Professor:

Royal Blue Overdrive offers a wide range of tones from light overdrive into distortion and at lowest Distortion knob setting works as an EQ. It can also be used to create tube amp-like crunchy ‘strike hard for distortion’ effect. There is not much filtering on the overdrive, to provide a transparent tone that you can tailor with both the Treble and Bass controls.

Like the best boutique amps, the Royal Blue OD lets you determine the amount of breakup by how hard you strike the strings with your pick, and/or by adjusting the volume knob on your guitar.  The Royal Blue can add this level of expressiveness to any clean or slightly overdriven amplifier.