Got my Mel9 last week.
All in all, I like it.
I’m having best results with adding some fx after it.

One thing I noticed right off the bat – it doesn’t handle Major 7th chords or similar intervaled chords. If I play a Maj 7 the top Maj 7 note will pull the bottom root note out of tune down to the Maj 7, and it seems to “confuse” the Mel9.

My other slight dissatisfaction is the constant vibrato on many settings.

My final issue would be that I would like there to be a way to completely eliminate the dry signal from the FX output, even when the pedal is off. Otherwise, my dry signal gets processed by any fx I happen to be running the Mellotron sounds through.

It would also be nice to be able to switch between Mel Instruments on the fly.