I just bought 12 for my 24' round. We've had a crappy May so far so it's hard to say how well they work. However they are not as easy to put on and remove as I thought. I thought the ring was made out of fiberglass but you just blow them up. They tend to flop over in a good wind. Once you get them out of the pool they're a little tough to handle.

BUT....it is a lot easier than the full solar blanket. Once we get a break in the weather I'll report back how they work out during the swim season.