There are mixed reviews for this product online and even on this website so I thought that I would share my experience here.
I live in a very warm climate and it is almost Spring here. Daytime temps have been approaching 80 degrees with lows at night in the 60's. My water temp has fluctuated between 60 and 64 degrees. So, in order to speed the process I bought some Cover Free at Leslie's as it was on sale.
So after using it for 2 weeks now I can safely say that it simply does not work. My water temp has stayed between 60 and 64 and it definitely has not slowed evaporation either. Now, that in itself is not the worst part! This stuff burns up my Chlorine, big time! I have gone from adding half a gallon of liquid chlorine twice a week to having to add it every other day. All other factors have been relatively constant (temps, no bather load, etc.).
So all I can say is don't bother with this stuff, not only does it not work, it costs you more in the long run due to excess Chlorine consumption.