It is a power attenuator with cable between the amp head or combo, or the speakers.
This is what the beast moved
Natural Tone Technology, clear high end responces
Available as 2, 4, 8 or 16 Ohm version
Attenuating 2db 2db steps from-16dB to-
2-step BITE and PUNCH Boost-Switch
"LOAD" position for use Without Speaker
150 Watt RMS (2 Ohm version: 75 Watt), With Control PEAK
FANTA-Out Speaker-Emulation, low Z, symmetric
Classic Amp-Cabinet Design with Tolex or Tweed ™
I took it into 8 ohms for my Soldano Avenger 100 watt settings with punch dick and really found his head directly into the baffle but with 2 to 16 dB less!
What is really handy knowing that a 100 watt head (even with a master like the Soldano effective) really does its juice to a volume set at noon.
I use it for live and repeat very useful for not killing the eardrums while keeping the "big sound that kills"
The Speaker-emulator is fairly accurate but I find that lack of momentum in attack ... it can help to model and replace a pod while keeping his true "tube"!
Super easy to use as far as one uses the same impedance to the head, the silence and the speaker is no danger of breaking your favorite amp (a little fan starts to cool the engine when "shot")!
The manual is very well done.