I think you should go proprietary with Otis GCS controls, Compass destination dispatching and Panorama elevator management system. It is the best stuff on the market right now. You and your tenants would be very pleased, it would probably be cheaper and definably more reliable. Thats just my opinion as a Otis tech.

BTW the prices these guys are giving are just to buy the controller, the much more expensive part is the labor to put it all in adjust and inspect.