The Ducks Editor Suite never really got beyond a beta test version and as such it's stable and functional, but a little rough around the edges. For example, after downloading it, you need to use it to extract some data files from Ducks before you can use it to make your own levels. But hey - it's free, and it's here if you want it.
Remember, if you have any problems or create some amazing levels then speak up on the forums and let the Ducks community know!