Product review (5 stars): Works great for my application
I used this as a sort of in-line damper in my hood vent.  I had to modify it a little since there are tiny knobs that don't allow the "flaps" to sit perfectly flush and a fin on the outer edge (assuming it's to attach to the hood it's designed for) but that just entailed 30 seconds of scraping with a utility knife.  Works great for my application