Some of the reviews complained these were not good vents but I believe they are described correctly. They have two levers that increase or decrease flow volume. They never completely shut off as there is a small amount of air that can always get by the two doors. The most difficult part of install was snapping the two halves back together on either side of the panel. The tolerances were so tight I struggled to get the third latching point snapped in. Will give them a try to see how durable it will be.
Rating: [5 of 5 Stars!]