The thing that stood out more to me than the n being low is "the participants reported not previously using noise to help them sleep or having any sleep disorders." Sleeping with pink noise seems like something that you'd end up getting acclimated to.

My n=1 is that I often sleep with a fan on and live in NYC -- whenever I stay in a place where there is no noise I tend to have trouble sleeping, so I end up turning on some nature sounds on my phone from myNoise.