As far as I'm concerned a heat pump is useless, unless of course your going to run it 24/7 to maintain a temp, which means your running your filter 24/7.

My sister has a gas heater.......... she can heat her pool pretty quickly........ though I cant tell you how much that costs her.

At this point, I only use my heat pump when my wife goes into the pool so that she feels the warm water coming into the pool. The heat pump I have is aqua comfort.