I've never used the original pedal and I'm not a Mayer-fan so I can't comment on how close the reissue is in reference to those sounds.
However I HAVE extensively used the amp it's supposed to mimic - the JTM45, nicknamed "Bluesbreaker" in it's 2x12" combo format after Clapton used it while in John Mayall's Bluesbreakers.
The originals were intended to bring the Marshall sound to cleaner sounding amps - i.e. Fenders.
So far I've used it with my `67 Deluxe Reverb and both singlecoil and humbucker equipped guitars.
With low to medium gain it's kind of a "leave it on pedal" that makes the guitar sound "cleaner" with a slight compression/distortion - very good for Dave Edmunds rythm sounds.
Not many buys a Marshall to play it clean though and if you turn gain past 1-2 o'clock IMO it comes very close to the amp.
So - is it a perfect substitute for a JTM45?
No - not if you want it to behave exactly like a tube amp, but I think it may very well be as close you can get without sploshing out 2 000€ (combo).
Handling - 3 knobs = easy to use.
Features - some may want 3-band EQ, if you already have a good clean sound this 1 tone knob is enough IMO.
Maybe we could ask for a version in a standard pedal casing for easier placement on standard pedalboards?
Quality - Sturdy, footswitch & potentiometers seems to be good quality.
