At least with the PSR 740 you can press one easily accessible button to turn on and off the vocal harmony. A footswitch would be a nice feature. I, myself, would probably not use the feature because I like to keep my setup time to a minimum.
But what if you do one song with a simple intro and simple ending and want to do the next song with different intros and endings. What I really fear is that for each song, to change this setting, I would have to go through a whole rigamarole. After I selected the style, I would have to go through a whole function menu to choose which intro and ending I wanted to activate, and then during the song, if I wanted to insert a different intro, I would have to, while singing and performing, go through a whole function menu to do this. This would just be intolerable, and would possibly turn me off of buying this keyboard.