Deffinitely agree on a good reel. I regret cheaping out on that.
Spend the money and get a good one, plan on a new solar cover every three years.

I dont have a lot of direct experience with varying thickness but the science of it says most of your heat loss is in evaporation.
It's been my experience actually that removing the cover during the day and covering it back up every night nets me the warmest pool...even better than keeping it covered with a clear cover 100% of the time.