From what I have read, including the US Gov site on energy and others, your pool loses 70% of it's heat through evaporation and conduction. If you look at the statistics of how much heat you will need or energy you will use with a gas pool heater, they will give you figures with using a cover and not. They are almost twice as high if you don't use a cover. So even if you don't get that much heat from the sun to actually heat your pool, the blanket will save the heat you already have. Especailly at night when tempertures can be 10 to 20 degrees cooler than during the day. And remember standard Physics is that heat always moves to something colder. I'm in refrigeration and that is how our refrigeration systems work in a walk-in or ice maker..etc. The heat in the walk-in will jump to the refrigeration coils because they are colder and the heat (energy) is then moved to the outside. Energy can not be created or disposed of, it can only be moved. So the heat (energy) from you pool will move to the cooler ambient air unless you have a cover to stop it. If you can stop that process with a cover and actually add a little (move some) into you pool with a solar cover, that would be even better. So I would get a solar blanket because you need a cover anyway. Just my two cents. You don't have to take it. Hope this helps some.
Aranon