They are especially bad in northern climates since the incoming water is cold, and they put cold air in your house - which then has to be heated by the home heater.
An A/C is already a heat pump.
it goes in an insulated tank? why does the speed matter? the tank is always at temperature. if you run out of hot water, that’s a tank size issue, not a heater technology issue.
But that's still just 4 showers - if you have a bunch of people all getting ready for an event, and you also have laundry to do (which uses double what a shower uses, although takes longer) and run the dishwasher, etc.
It's not enough. You would need a truly mammoth tank.
Instead you have a large fire at the bottom, and heat the water almost as fast as you use it, then you don't run out.
A heat pump water heater would simply not work for a 6 person home in the north in the winter.
That is desired, and apparently is not actually the case. I did my research and that's what people tell me, so I didn't get one.
They might work better in hotter climates, but in northern ones with incoming water near freezing, they don't.