as for me, I would have never tried to insist, that someone's opinion connot be taken serious, if he played keyboard in a shop. Instead, I would have explained him, what he can do better in order to use all keyboard's features in real time.
How can you explain me the facts, that
1) if you want to include Fill-In without changing style type, you have to push twice button which lies in the middle of the keyboard (I would place it to the left)
2) if you want to make 1) + change variation, you have to push twice the Fill-In button and touch the upper part of the screen, which is more farther from the left part of the keyboard
3) if you want to make 2) + change One Touch Settings, you have to push Fill-In twice, touch the screen, push OTS button and touch the screen again. Then you will probably have to push Style button, in order to see the variations screen.
4) if you want to make 3) and change some sounds with your mentioned style-morphing. You have to... you know.
And... please do 4) in real time during your performance.