We bought two (as the best option we could see on the Omlet site) to fit over an Eglu Go-Up and try and prevent the ground looking like the Somme. They have certainly improved the situation with all the rain we've been having lately so thats the good news.
However, the eyelets have rusted within a few weeks. Due to the design of the go-Up the rain still get's in under the coop and around the edges of the cover so the ground is still fairly wet and muddy. The "Clear" plastic is now filthy as the chickens flick muck around (admittedly we could take the covers and wash them down).
In the short term the covers have improved the situation for the chickens. Longer term I will probably build a permanent roof structure over the top of the Go-Up and run to keep the chickens dry and mud free.