I was thinking something similar about the SMK37PRO but then was very disappointed about of what i found inside the instrument (nearly nothing) only a tiny custom "unbranded" chip.
That's interesting:
https://www.viscountinstruments.com/products/professionals/piano-keyboards/legend-70s-keyboards/fm-synth-module/
A big Piano manufactorer has a FM module in his program, which specs are very close to Synth_Dexed / MicroDexed...