Spec'd as a low-gain transparent overdrive, the Messner is designed to allow the tone of your guitar to shine through.
It's also one of the subtlest overdrive units we've ever come across, even with the gain control at full tilt.
In the 'closed' position, the mini-toggle switch engages the internal clip diodes for some extra breakup and compression. This mode responds to the dynamics of our playing beautifully, unleashing some extra bite with robust rhythm work.
Think Mike Campbell's sound on Tom Petty's American Girl and Refugee for reference.