It's a 6 voice, 4 operator synth on which you can modulate the operators any way you want, meaning that you can create some amazing sounds. However, the rest isn't that inspiring for me. Filter is so-so. Onboard effects are not great, especially the reverb. And I'm not a huge fan of its sequencer, so I use Digitakt for that.
I would give it a much higher rating if the edit mode supported MIDI CC for making changes, instead of sysex dumps, as that would make it awesome for live tweaking with external gear.
If you really need a portable FM groovebox under 300 EUR, this is probably it, but maybe saving up for a Digitone would be a better idea.