I would develope this UI to little more user friendly. Currently it is not as bad as most FM plugins out there, but this still has some flaws.
Like there is too many buttons in toggle mode. Example filter mode and all those curves.
Now if one toggles one too far, it is needed to go through all other choises once again.
I would solve this with preferencies button which would open separate window where user could choose which way they function.
One another usefull setting would be size of the whole UI and size of the pots. They are quite small now.
Operator waveform is one more toggle that i would replace with mouse over menu or “popup” menu as in OP order.
Anyhow i liked this more than most other FM VST’s and i was not just critizising, but tried to give constructive and honest feedback so that programmer would really know what (some) users really think. Instead just saying “nice” or “awesome”.
Oh, and i liked presets! There was much enough and some of them very really good.
I am not a “preset guy” but i like to use those as starting points and of course, to see quickly what plugin is capable of.