Personally I don't like the way the back window looks on the D40 pics, someone else here also mentioned that they had trouble replacing a bent window in their canopy, so that may be some fuel for thought.
Not sure what they mean but pop out windows on the side but to my thinking it means the windows only pop out at the back and give you about 2 inches to push stuff through, even sliding windows do better than that. I also reckon a rear demister is a waste of time given that the back window can be as clear as you like but if the sliding window is fogged up you still wont see past the fog. Opening the sliding window or the side windows should remove the fog anyway.
I actually think you can do better for a similar price but thats just my idea.