The product works superbly well - v wide wifi coverage and v fast hence 5 *.
However I did have set up problems and having researched on the web found out I am not alone. Following is a summary of the problem and fix incase you have the same.
I have an existing devolo network with dlan plugs. Added these new wifi ones and the network could not recognise them. I also kept getting a network key mismatch message when trying to enter the passwords printed on the devices.
Download the latest devolo lan cockpit software from their website (don't bother with the disc that comes with the devices)
Remove all existing devolo lan plugs from the network (if you have any)
Attach each one in turn directly to your pc with the supplied lan cable and use the cockpit software to "reset to factory setting"
When resetting the wifi extender one change its network key to one you will remember - you can do this via the devolo software
Once done attach the new router one from this kit to your router and plug into the wall
Then plug the other wifi extender in to the wall and enter the network key as required
This should fix everything - you can then go and add all of the other plugs if you have them.