I saw an old thread with a clip of the NPN boost, but the links are all dead, so I figured I'd post a clip in case someone wants to hear it before they build it.
This was recorded with the boost at twelve o'clock. The guitar is played without boost first, so that you can hear the distinction. The setup was:
79' gibson paul -> NPN boost -> garageband software
I guess it's debatable whether it's better to use an amp to record clips for the sake of honesty. In this case, the boost sounds good going line-in. It's nice that it's not only a learning tool but also a very good sounding and usable effect.