Product review (5 stars): High quality, robust, and good design!  They are 6.5x6.5" for the outside edges, be sure they will fit your application.
We haven't had them installed that long, but so far they are great.  We replaced 3 old 3-flap plastic bathroom exhaust vents on the side of the house with these.  The old ones were noisy and would clack around in the wind, then I went to remove them and they disintegrated in my hands (and had bees nests in them!).  I wanted to replace them with ones that would provide better resistance to opening and would stand up to the hot sun and heavy winds (it gets windy here).

So far, they stay closed for the most part except in very heavy winds; to be fair, it would be impossible to stop it completely with 35+ mph gusts, but even then they have done a great job staying closed and quiet.

One thing - BE SURE TO READ THE DIMENSION SPECS!  Most vents are about 6x6" (the plastic ones at Home Depot or Lowe's for instance), but these are indeed 6.5x6.5".  I had to take and angle grinder to them to trim them down to 6x6 to fit in the recessed area where they mount on the house.  The product details DO say they are 6.5x6.5 - just be sure that they will fit your application.