I have seen those demos....I wasn't impressed at all.....
IMO it's a toy gimmick...Yamaha has alot to learn with VH processors...that's why so many players have separate units like TC Helicon Harmony M, Etc, Etc, even though they spent thousands on an arranger KB...go figure?..
btw... I really enjoyed the vocoder mode this demo showed on a great classic Queen song.....it was really well done. I'll also agree that many players have no idea how to use VH effectively and over use is an understatement. Used sparingly it certainly can enhance a song when done correctly.
Studio recording is how I like to use it also..