It's a load of BS. I didn't even have to click the link. I know what it is. It's 2 jacks and a 100k analog pot. That's it. I built one from Radio Shack parts for less than $10. They are best for amps with VERY sensitive master volumes (like Fender's) where 1 is still to damn loud. Put this in the loop and set the MV to what you want and adjust the volume box accordingly. It does NOT push the power amp tubes any harder.