The sole minimizes the irregular surfaces on the bottom surface of the foot. The shoe also protects the feet and toes. If you feel uneasy about the investment at first, you might try a pair of more ordinary shoes that meet as many of the requirements as possible of the ideal organ shoe. Either way, the pair of shoes you choose should be set aside for this purpose to protect the pedal key surface from damage caused by floor grit. The heel surface should allow the heel to slide easily forward and back on the naturals without leaving marks.
Leather is usually best.
The sole should slide easily up and down the keys, and from sharp to natural. The uppers should slide against each other without sticking. Organmaster will exchange shoes until the right fit is found, as long as they are not scuffed or blemished. Dance supply stores often carry shoes that work very well as organ shoes. Women's Capezio 450.