Hi spider - I'm not one of those trying the "No mucolytics" trial. I tried it years ago and ended up with yet another 4 month long ear infection followed by a sinus infection.
Thanks @scoop for providing the link - after watching it twice, I am not convinced that a single opinion outweighs all the studies I have seen, nor my personal experience or that of many Connect members.
Keep in mind that most of us have not had the extensive testing done at NJH, so may have ant number of genetic markers or proteins that indicate a predisposition to Cystic Fibrosis. Given that I have had ONE exacerbation during three years of NAC (compared to dozens before), have a daughter who is positive for the CF gene (though she does not have CF)) and that other studies show the merits of mucolytics, I will continue to use it until it is demonstrated conclusively to be detrimental.

So, my non-medical, non-expert takeaway? We are all different in our Bronchiectasis journeys and our responses to ALL treatment modalities - antibiotics, beta agonists like albuterol, 7%n saline, alternatives like NAC, airway clearance, exercise...
If NAC or Mucinex help you, and you are not having frequent exacerbations or side effects, and do not have contraindications (certain cancers may be aggravated by it) go ahead and use it. If not, continue to explore other options.
Sue