Product review (4 stars): Very nice, but installation issue - read review
This unit was what I was looking (actually my wife) but it doesn't work exactly like the picture shows.  (not sure what the 6" thing is about since it is just for 4" piping)  The issue is attaching the wall part of the fitting to the metal duct pipe which is on the other side of the wall board.  Basically the situation is that the metal ducting is between the studs and then the wall board is applied.  The wall fitting of this unit pushes into the metal duct and then screws to the wall board as shown.  The problem is how do you push the wall fitting into the duct pipe since if you push on the metal duct it will likely recede into the stud space since it would not be possible to secure the duct to the back of the wall board.  My solution was to place some wood in back on the duct elbow so it could not recede and then carefully set the elbow such that it extended 1/2 inch or so beyond the plane of the studs, sort of like an electrical box.  In this manner, I could then fit the wall portion of the fitting into the duct elbow without it moving since it does fit tightly (which is what you want).  If you do all this, then it will look just the picture and it's great.  Sounds more complicated than it is but you will really regret it if you do not do as I say.  They really should have three parts, the third being a fitting that attaches to the end of the duct elbow and screws to the stud face (again like an electric box).  Having said all this, I am an engineer who thinks like this and tries to improve everything by making it more complicated...  (note there are some docks that combine all this into one unit but I like the way the dryer tube attaches to the wall unit portion.  Looks very nice once installed)