We use the mask. For one thing, if your child isn't totally concentrating on breathing out of their mouth, then more than likely, they are breathing through their nose and the med isn't going deep into their lungs anyways. Mel and I had many conversations about the difference between the two.She used the mouthpiece, but, realized a lot of times, she would catch herself breathing out of her nose. She highly recommended keeping Zoe on the mask until she was much older. Also, Zoe has a lot of sinus issues, she was put on Hypertonic 7% bid, so, with the mask, she is getting the solution through her sinuses.