There needs to be a balance when it comes to the weight of it as you want it to be heavy enough to stable but light enough that you are going to be able to move it fairly easily when your pool is uncovered.
The recommended weight is going to depend on the size of the cover reel that you need, as the larger the coverage is, the larger the reel needs to be. All the products that we have looked at here strike a great balance between weight and maneuverability.