Omnisonic Volume Control Box??????

anyone ever use or hear of these?!?  I have a Marshall JCM2000 dsl100 and I need to get a power soak or something to play it at home...but I saw this volume control thing that swears it controls volume so you can crank your amp, not lose tone, etc.  It's only $30...has only 3 reviews on harmonycentral's website (which it scores almost a 10).  There has to be a catch? or not?!? 

help!!!