People are different, have unique comfort expectations and lifestyles.  More often then not, hot water circulators with fixed temperature set points do not match the homeowners ideal comfort temperature.  Additionally, most manufacturers choose to avoid the significant additional cost required to produce more efficient products.  Inefficient products are almost always the cheapest priced products.   their hot water circulators temperature setting to their optimal comfort standard they have no choice but to continue the routine of waiting not just for hot water comfort but now even cold water comfort depending on the technology / cost invested.  Wasting energy and resources is directly dependent on how long a person waits for their desired temperature of comfort.  The longer the wait, the more water goes down the drain and the more cold water enters the water heater to be heated.  Installing a hot water circulator with a fixed temperature is like betting on double zero's in craps, hoping it's your just right comfort.