So, I did a price comparison on water heaters since I may have to replace my electric water heater soon, and uh.. wow, the average energy usage difference in cost is pretty crazy. Prices are based on what I pay for natural gas/electric in my area in the states, usage is how many kilowatts/therms (1 therm is 99976.1 BTU) get used per hour. Daily usage is an estimate of how many hours each device uses per day.
Okay so it turns out the hybrid water heater does have 4.5kw elements inside of it, but I'm guessing that those are kind of like emergency backups to help keep up with unusually high demand. So while it is capable of pulling 4.5 kwh, it'll still use on average maybe a little over half a kilowatt.