Haaa, finally tested these with a MIDI keyboard. The sound set is rather uneven: nearly all synth pads are quite good, some excellent, part of the strings are great, while any blown instrument sounds highly unrealistic at best and pretty crappy at worst. The percussion is good to great, but the pianos, chromatic instruments, and anything else with keys are rather boring. The string instruments that aren't great aren't great because they sound like keyed instruments. There's something weird going on with the sustain part of the envelope on patches with long sustain, likely looped samples (in some cases you can hear the tail end of the attack for a bit when the sample loops).
There aren't many options to modify the sound: modulation, pitch bend, main volume, pan, expression, sustain pedal, sostenuto, soft pedal, most available via CC. There seem to be some more options available via (N)RPN messages, but the instructions for that are almost entirely in Japanese without sysex codes.
The microphone volume needs to be turned up quite far to hear anything, and I cannot get the digital echo to work.