Maybe I am missing something, but I use the VH on my KORG Pa900 and I don't find it difficult at all ... I only use a couple of SMFs, but I've set up specific styles for songs, including the harmony voices I want, without a problem (I have created a number of different harmony 'presets') ... I can also change the harmony parts "on the fly' while I am playing a style ...
I don't think we can REALLY hear how the harmony sounds while we are singing, but I have had many compliments on it, especially from my most sincere critic, my wife ...
The only other VH I have used is the Digitech VH Workstaion ex, which also sounds great ...
Just my 2pennies worth ...