Mike, I'm saying that the harmonizer in the Ketron SDs is very good. They do everything I need. I feel no need to use an external unit with them, as I do Yamaha.
In addition, they do gimmick voices and choirs.
I'm using a Midjay most of the time now, and the Harmonizer in it is strictly a Vocoder, so the external unit is necessary for me.
It IS neat to have the Harmony M setting right on top of the keyboard where you can easily change presets, voices, adjust vocal processing etc.
Two harmony voices are enough for me; may not be for everyone.
DonM