This one is a dual booster in the spirit of Nigel Tufnel :) It has a modified Rangemaster circuit with NPN germanium OC140/CV7112 transistor and a 3-way tone switch into a ridiculously loud mosfet booster. You don’t need any more volume than this. Seriously.
If you want slight grit and Rangemaster tone you could keep it on all the time and just boost the signal with “more volume” channel when needed. Rangemaster also cleans up really well with guitar volume so you could just crank up the “volume” channel and control the amount of boost/grit with your guitar volume. Handy!