Thinking of checking one out primarily for the Marshall YJM. The Power Reduction works well but I believe an attenuator will see the actual power from the amp and sound better.
I use the Rockcrusher with an insanely loud Cameron modded Marshall. It's the only attenuator that I've found that can lower the volume to bedroom levels for this amp. I don't seem to lose any "power" from the amp with this. It still sounds angry. Love mine!