I'm thinking of buying another for the beginning of my chain as a buffer with bright switch engaged ...or as a volume boost in my effects loop

The second (right) DIP switch is a "bright" setting.

boost internal switch off and had the external knob just above the absolute minimum).

It warms everything up and adds a sparkle with the bright switch on

If you turn the bright switch off, the tone become darker, which was a characteristic of the original vintage Echoplex circuit.

Default is 3+ gain and bright switch on, but I switch both off to keep it at unity in "vintage mode" and when I turn the pedal off, that in your face sounds falls away