People are often advised to not lock their knees for a long time while standing (ex: marching band, or standing at attention in the military), and you cannot force anyone to have healthy posture. The ergonomics of these seats appear to take some of the load off the legs and feet, but it’s something to consider for patrons with more sedentary lifestyles. Many people believe themselves to be fit individuals until they are placed in uncomfortable conditions for a long time or experience unexpected stress. They could manage to injure themselves in some way, then find some reason to litigate.