This could also depend on the pool setup,
Is it enclosed ?
Do you want to swim 365 a year ?
Do you have a good thermal pool blanket ?
What temperature do you intend to have it at?
I only swim about 8 months of the year so simply turn the heater off during winter. I wait until the forecast is for 3 hot days in August/September and then turn the heat pump on, take the thermal blanket off run it during the heat of the day and afternoon. When the sun drops off I put the blanket back on.
If the weather is cool/cold the heat pump is slow to heat the water, though it is still better than the old solar heater.