The systems are more popular in cold climates like here in MN.
FYI: It's -10F here right now.
Here in MN there is one company trying to market a "air source" heat pump, but it's quite complex and expensive. Normal air source heat pumps don't work when it's cold out. I tried to get them to market it as a "portable" system where you own it like a car, but that would require them to re-program the computer so that it could also cool the water heat option it has.
The MN DNR rules don't allow you to use two wells, you have to either discharge at the surface or use what is called a "clean water drain field"
The "pump n dump" systems do have one drawback in that every few years you have to wash the unit out with a cleaning solution (like vinegar) to remove the mineral deposits.
The well and trench systems have very little maintenance, but cost more to install.
All in all These systems are best way to heat a house and when combined with low priced electric from either "Dual fuel" or "off peak" you get a very low cost way of heating.
I would put one in if I could afford it.
But I keep paying the ~$200/month for baseboard electric.
PS: This topic may be better in the HVac section. *You were right, Cookie