They do have more parts, but these units are basically a heat pump mounted on top of a water heater. It's more complex but not absurdly so. There are only four

They do have more parts, but these units are basically a heat pump mounted on top of a water heater. It's more complex but not absurdly so. There are only four manufacturers who sell hybrid heat pump / electric water heaters in the US. Other brands are rebadged. Namely: Rheem, AO Smith, Bradford White, and Stiebel Eltron All four brands offer 10 year warranties. Heat pump water heaters have very slow recovery rates compared to gas, so I would buy the largest unit you can fit. That's usually 80 gallons, but they are very tall (due to the heat pump) so it depends on the space. UEF varies from 3.3 to 3.7, and prices range from $1700 to $2400. The lowest TCO is a Rheem unit at an estimated $3310 over 10 years (purchase price + electricity). Rheem is currently ahead of the others on efficiency and Stiebel Eltron is probably going to be difficult to find service for in the US. The other two are middle of the pack.