I've used this a few times, its a 4 operator FM synth with variable waveforms in the spirit of the TX81Z, but they added a master fitler with an envelope gen as well as really advanced LFO features not present on old Yamaha hardware. The interface has a helpful graphical display of the algorithm operator routing and the knobs make it feel a lot ore intuitive than hardware FM synths. The sound? Its okay. The filter model aliases a bit at high resonance, especially when assigning cut to a wheel and sweeping.... its state variable and not all the modes are created equal. There's a passable chorus that I wish had a bittier, early digital quality like an SPX90 chorus patch, but all in all a good tool that does different things than my DX7. While I could make similar patches in sytrus, the streamlined FM4 interface makes it faster and its a lower CPU hit. This has made the cut in a couple of songs over the years for keys layers that are more 'background'.