Product review (3 stars): Small and birds will get in.
The item itself is fine and well made. Depends on what you want it to do. One it is too small for the normal vent sizes on homes. Secondly it will not keep any type of insects out.  Especially birds.  The birds is what I wanted to keep out and I can see from looking at it that those birds will laugh at it and go in and make a nest.