Here is a link to the published article, complete with tables, that I found easier to read:
https://publications.ersnet.org/content/erj/62/1/2202053
This is the European Respiratory Society conclusion after reviewing thousands of studies:
"The current evidence supports that ACTs are an effective treatment and have a crucial part in the usual care of adults with bronchiectasis. Accessibility to ACTs should be facilitated and ideally delivered by a specialist respiratory physiotherapist. However, there is limited evidence establishing the physiological effect of these techniques and current clinical practice based on geographical regions remains largely unclear. The use of data from large patient registries could help to better understand ACT practice globally. Randomised clinical trials indicate that ACTs increase the expectorated sputum, improve disease symptoms and HRQoL and reduce the risk of exacerbations, although they often have an unclear risk of bias or a poor description of their techniques. There is a great need for studies to investigate the role of ACTs during acute exacerbations of bronchiectasis and in the long term. Additionally, researchers can consider different settings, new modes of application and novel outcomes for future ACTs studies. Importantly, to achieve optimal care, study designs need to incorporate patient-centred outcomes and patient voice."

I will offer my own "study" - In the three plus years since I have been 1) managing my asthma properly and 2) doing daily airway clearance (using 7% saline for some sessions) I have gone from 2-3 exacerbations per year requiring steroids and antibiotics to 2 exacerbations in 39 months. During that time I have traveled extensively, been around lots of kids and older people (both groups are great at spreading their germs), and had a bout of Covid.

Scientific studies or not, I am convinced.

BUT what did interest me is that NOT ONE of the cited studies in the tables recommended trying to get rid of "every last bit" of mucus. So I stand by the advice of my very first pulmonary nurse - never more than 20 minutes per session (after the neb).