I got one and put it together last night. great
about $60 total for everything, and about an hour to put together. I didn't buy a flange. I used a 5 inch to 4 inch reducer and cut the 5 inch side to custom fit the inlet of the blower, then folded tabs over inside it. that part was easy enough to do. then, I used a curved oval elbo with a 6 inch opening at the other end and added a 6 to 4 inch reducer to that, and cut and shaped it to fit the outlet of the blower. I used a small drill bit to predrill screw holes to lower the chance of cracking the plastic. I used plenty of normal sheet metal screws to hold everything securely together, then some duct tape to make it air tight. I'm borrowing a camera, so I'll have pictures soon.
my final review, I think this project is of great value. I'm sure the power of the fan is near that of what the pro's use. it can almost be used as a shop vac, and you can feel a lot of air movement from 20 or 30 feet away even on low. it should have more then enough power to cool HID's and scrub with a carbon filter at the same time, in a small grow room. the shape of it's frame makes it easy to grab-and-go, or mount/hang within minutes. my only potential con is noise. it's no louder then any other fan on display at walmart, and I even watched stargate atlantis with it right below the tv on low. but, for a stealth room, like what my project is, it might just barely be noticeable from outside the the room, by the exhaust. my room's not ready yet, so it hasn't been tested, but I'm sure I can make it work. putting the carbon filter in-line, after the blower should kill 99% of the sound and work perfectly, just the way I like it.
thanks potlike, for the great link!