Product review (1 stars): Poor quality, you need lots of tape.
The idea is great, and it can potentially save you about half to max 1 inch of space.
However, this product is built very poorly. If you decide to buy this, make sure that you also buy lots of heat and moisture resistant vent tape. You have to use tape all around it otherwise it leaks air. I used a lot of tape, but I am still not confident if it can hold up. I am going to give it sometimes.