Hi Zscline,
I began with 3% saline to test it out. I used it for a few weeks and it was fine. I the graduated to the 7% and have not had any problem with it. Breathing in the saline mist causes me to cough which helps clear my lungs of mucus. I nebulize and use the Aerobika together. The device hooks right into the nebulizer. Below are links explaining about Aerobika. It has been a real game changer for me. Best of luck to you!
https://www.mskcc.org/cancer-care/patient-education/how-use-your-aerobika
https://www.nationaljewish.org/conditions/medications/airway-clearance-techniques-devices/using-the-aerobika