Turns out Daox is right. According to the guys at SimplySolar who've done side by side comparison tests the aluminum downspout collector isn't as good as the aluminum screen collector. It's still works, just not the most efficient. It's more efficient than the pop can style though in terms of how hard it is to move air through it. I'm still building the downspout collector though as I've got to mount it horizontally, where screen collectors lose a great deal of performance.
Xringer hide the fry pan.