Product review (1 stars): DANGEROUS FOR GAS
Have a gas dryer, this item has too many openings that leak carbon monoxide into the room. Probably okay for electric dryers, dangerous for gas.

It reduces the airflow from the dryer since half of this adapter is internally blocked by design. Raising backpressure and making leakage worse.

I'll keep my dryer 4" away from the wall, the 2" saving isn't worth the risk.