Really cool design! Love seeing instrument manufacturers to come up with new ideas.
Just a shame, as HTH said, 9dB isn't that much. You can't get a plexi or even a 18W to break up at -8dB setting on the THD Hotplate at home volumes. More for stage use it seems. Might be able to get great results if this was combined with another attenuator since most attenuators work best in moderate attenuation levels. If the speaker itself sounds good, this could be a winner!