I'm a huge fan of prog music.
I grew up with the keyboard sound of groups such as King Crimson and Genesis, and PFM (I'm italian). Only in recent years I undestood the important role of Mellotron in this music but, alas, i'm only a guitar player so the Mellotron was not wish list. When I heard of MEL9 i could not believe to my ears: i could play mellotron sounds directly from my guitar, without using any MIDI esaphonic pickups. I own several MIDI esaphonic pickups for guitar, including Roland GK-2 and Fishman Triple Play. Each one features some latency and some incorrect note detection, and needs additional hardware (PC and/or Sound Generator) to produce sounds, so I use them not so often. The great advantage of Electro Harmonix MEL9 versus MIDI esaphonic pickups is that it does not require any extra hardware to produce keyboard sounds. I still don't undestand which technology has been applied, but it works. I simply connect my guitar to MEL9, and as I play I hear tipical mellotron sounds coming out of MEL9 with virtually no latency.
I tried it with both electro-acoustic steel string guitar and electro-acoustic nylon string guitar, and the result is good on both type of guitars.
About the sounds: some sounds are really convincing, especially the "Orchestra" sound which we hear in many Genesis and King Crimson historical tunes. Other sounds are far less convincing, such as "Cellos" and "Brass".
On the negative side:
1) this pedal is raher pricey, so more sounds would be appreciated. Also I would greately appreciate an USB connection to PC for modifying envelope curves and timbre.
2) The pedal switch is very noisy, so when I turn it on / off in my room al low volume level, the acoustic "click" is too much loud for me.
3) The MEL9 is able to effectively convert only notes played rather loudly. In softer phrases, the converted sound is slightly out of tune.
4) The only way to switch between the presets is via the dedicated rotary knob. A dedicated preset switch would be appreciated, especially during live performances.
However all these negative sides don't prevent me to enjoy playing it very often, and I recommend it especially to lovers of classic prog music.