I tend to be VERY skeptical and would not have bought Cover Free. I went to a new Leslie's that just opened and since I bought a 3 Liter bottle of both Pool First Aid and Pool Perfect, I got a free Quart of Cover Free with purchase (Grand Opening Special plus 20% off).
I can't explain how these things work but I can say that Cover Free from Natural Chemistry works. I have always been impressed with their products and it looks like Cover Free works as well. I added it to the pool and had a 5 degree increase in temperature in just two days with it going into the 50s at night. I guess by not letting the night air steal so much heat it is actually able to allow the pool to heat up quicker due to retention.
As to it staying on the surface, it uses surface tension to stay on top of the water surface. It is not all pulled into the skimmer and pump unless you have many time more pump then you need and have a flushing vortex in your skimmer box. And since the dose is measured by your pools total gallons not surface area, what does get pulled in resurfaces when it re-enters the pool from the filter. Also the time its most needed is at night, so the first time you use it, use it at night, turn your pump off and then add the product to the surface. It is suggested to retreat once a week, which I do every Thursday Night.
We have been swimming for three weeks now and I have never been swimming this early without using the heater, dome, and a full solar blanket!