I regularly have problems with the ios and Android apps not downloading or connecting, and generally just work with them "offline" with my few successful downloads.
I use the sleep music whenever I travel, combined with my Bose QC20s it's great for blocking out aircraft noise or even as I discovered on a boy's weekend the snoring off my bunkmate who people in other rooms complained about.
I don't know about their scientific claims, but for me it does what I want, which is distraction free blocking of the (audible) world around me.