Operates at much higher pressure - 600-1800 PSI. COP is 4. [1]

Sourcing

SanCO [2]. Down to -20F. 5x more efficient than electric heat for water heating. Appears workable, ROI in 5 years, [3]. $5600 for a hot water heater. [4]
Goes down to -4F [5]

Other

There are heat pump water heaters available. This one uses backup resistive (1.5kw) and heat pump (2.2kW) heating. It's a hybrid heater. [6]