i assume this pedal wouldnt be too great with a SS amp correct?
you are absolutely correct.
what would the difference between this and a EHX double muff be?
someone once referred to LSD as liquid sunshine
It might be good, actually. It's a JFET design, so you might be able to use the pedal to distort rather than the amp. It depends on the amp, I suppose, but you might have some luck with it. It's very different from the double muff, which is a modern fuzz.