Product review (5 stars): Works nicely. Seals well.
I bought this to replace an existing one that went missing, and didn't bother to use my brain.  ProTip:  6 inch hood does NOT mean its 6 inches wide/long...
Yeah it means the big circular thing sticking out the back is meant to go on a 6 inch pipe.  My pipe is probably 4 inches, though its recessed back a bit.
You cannot actually see the big circular thing in this picture, tho I suspect they all have one.
All I saw was that I had no cover and there was a 4 inch round hole with plastic around it with 4 screws in each corner.  And turns out the screws were not even used as you can't exactly screw easily into brick, unless you have small tapcons laying about.

So I wound up using multitool to chop off the circular thing on back and glue it on.  Then caulk the heck out of it.

OK, so even I am kind of missing the point of this review so far, but the product does work...flaps freely and seals decently well when not blowing.  So I am happy, even though I kind of bungled it at the begonning.