You do not appear to be reading this right.

Here lemme break this down and slightly rephrase it for readaibility:

Compared with the control group[,] in the didgeridoo group [we observed] daytime sleepiness and apnoea-hypopnoea index improve significantly.

[Their] partners reported less sleep disturbance [as well].

There was no [discernible/signifcant] effect on the [self-reported] quality of sleep.

So what you describe as 'masking daytime sleepiness' is actually just 'less reported daytime sleepiness'.

IE, you're more alert, less sluggish, when awake.

Apnoea-Hypopnoae index is basically the time you spend during sleeping having blood flow oxygenation below critical levels... this also significantly lessened.

Meaning that people got more regular well oxygenated blood flow while sleeping, after blwoing through a tube regularly.

The only thing that did not improve was self reported 'quality of sleep'.

Yet they were observed to snore less, and reported being less tired during the day, and their sleeping partners reported being disturbed less.

So, the only metric that didn't improve was the one that is the most subjective and least important.

They didn't report 'better sleep' but... everything else indicates that their sleep was indeed of greater quality.

Psychosomatic dubiousness that anything is different vs every other metric showing improvement.

Or, your response, basically.

Going back to the numbers, the day time sleepiness index is from 0 to 24, where over 11 is excessive sleepiness. The mean improvement is -3, which basically means these people got 3 more useful active daytime hours a day, they got 12.5% more useful time in each 24 hour period.

Again that's not masking, that's the exact improvement you are looking for.

The 'choking in your sleep' index improved by -6, when the average score of all was 21, so basically the average result was roughly 25% less time spent choking in your sleep.

Who would opt for this treatment?

I dunno, maybe anyone with a CPAP machine that wants to one day maybe not need a CPAP machine, or someone with a CPAP machine and also an unreliable local power grid?