Lower saline strengths do not have as much effect on NTM, but some people on this group have had success tolerating starting with 3% and gradually increasing strength by mixing with 7%. In addition to effectiveness in suppressing bacteria growth, there is good evidence that 7% saline is better at thinning mucus than airway clearance (ACT) alone, a bronchodilator plus ACT or a bronchodilator plus .9% saline and ACT.
https://www.sciencedirect.com/science/article/pii/S0954611104002057
My pulmonologist says with "stable bronchiectasis" (no active infection and no recent exacerbations) As my primary would say "something is better than nothing." I am not sure I need all 4-5 ml in one sitting, it is just the "traditional" size of vials made for nebulized substances. I stop nebbing when I am getting up the mucus, then rinse and gargle with plain water. Someday I hope to find a study that talks about how much is is really necessary.

Have you tried using your asthma inhaler before nebbing? Sometimes that helps with the tight feeling.
Sue