Palmer PDI offers tp play on lower volume on tube amps but with full saturation and gain - an absolutely crucial function when You use smaller tube amps in a home setting and want to get the most out of your amp.
Important note! Be sure to check the Ohm value of your speaker from your amp to buy the correct PDI, 4, 8 or 16 Ohm.
I am not sure it works as well on low wattage amplifires as on high wattage ones. Palmer usually has good customer service and will answer your questions, being a smaller german company.
Summary: Usefull, easy and sturdy tool.