Winterizing the lines, leaks, and the added weight are the downsides to this. If you are in a climate where you don't need to winterize, you are probably in a climate where you can get away with a heat pump on your water heater/pool/AC. In fact, they make AC adapters that dump excess heat into the pool.

I really want this to work, but heatpumps just make a lot more sense with a lot less cost.