One of the sailing magazines ran a scientific, sort of, test in the last year if I recall. Compared all of the major wind generators, the D400 is it from the Duogen guys? and the Duogen itself.
I think the D400 was better than the Duogen, but of course the reason you have a Duogen is to shove it in the water as well.
I had a duogen on my previous boat and on current boat I have the Rutland 913. I found that the duogen was great for charging when in water mode but once at anchor in a sheltered spot you needed a decent breeze to get anything useful from it and I was then more reliant on solar to keep things charged. The Rutland on the other hand seems to put charge in constantly unless there is no wind at all for which I have a small solar backup.