This is a generic load box designed to connect an older guitar amp (without a line out) to a mixer or headphones. It can handle a maximum of 50 watts at 8 ohms. Great for silent practicing.
It is designed for amps that don’t have a line out. This box connects to a speaker out jack and places a load on the speaker to avoid damaging the amp. You can connect the box to a mixer or headphones for quiet practice. Since it is a generic device, it requires some tweaking of the volume controls on the box as well as any connected device (amp, mixer, etc.)
I bought it from an electronics expert some years ago for $150 and only used it a handful of times. I upgraded my amp setup and no longer have a need for this.