I've got one, and love it, I have a Sniper-modded GE-7, but even after the mods it doesn't come close to the ease of use, and range of sound of the PQ-4. Over the years, it's been the one pedal that always stays on my board.
I have one that I don�t use yet, but im about to have it as a linebooster and to modify the sound from the amp a little brighter. It�s a old ac30 from the sixties and it is a little dark in the tone. So I think this gem vill fix it. I tryed it at home on my Fender Pro Jr with the original speaker, and I thought that I came close to manipulate the sound to be more like "blue speaker" tone with this pedal. Only by some small changes. Basicly by increase bass and treable and put on some presence at the top. I think its great.