An actual data point - my heat pump water heater has been in use 2 days short of 10 months. It has a decent app that tracks power consumption - During that time, it has used 784.5 kwh. Set on heat pump mode the entire time. Average is easy - about 78.5 kwh/month. No hard data on my previous water heater power useage, but I've read the average is around 350 kwh/month.
It's in my basement, a semi - heated space. In winter, the temp in the basement around the heater can drop down to 48-50 F. At this temp, recovery takes a bit longer. Just 2 of us, not an issue. Appears to be plenty of space to use hybrid mode seasonally to address that if need be, and still realize significant power reduction. I sure noticed the difference in my consumption quickly - it got me over the line between using some grid vs self powering for some of the summer months.