Product review (4 stars): They are great at redirecting the air out from under the shelves
I have 2 of these vent extenders that I use under shelves. They are great at redirecting the air out from under the shelves. They are adjustable so if you have a deeper piece of furniture you can extend it to about double the length. My only complaint is that I wish this was a little bit wider. This extender covers most of my vents but not all of it, so some of the air still gets "stuck" under the shelves. My 19 lb toddler steps on one of them a lot and it has not broken or cracked, which surprises me since they are not very thick. Overall, this is a great product and it has allowed me to arrange furniture the way I want it and not be hindered by a vent.