I'm an avid music listener and this app is awful, even if I did have NSO. The library is pathetically abysmal and microscopic, listing only recent titles or the most popular ones (and even that is woefully lacking); I can pick a music I like out of a hat and chances are, it's not even in this app at all (DK Rap from Donkey Kong 64, there you go, that was literally out of the top of my head), plus the music list is bloated up by jingles and fanfares.
The worst part about this is that you use this app to listen only to Nintendo music, and nothing else. You cannot use this app in tandem with any other music, let alone, any other video game music not by Nintendo (no Sonic no Crash Bandicoot no Persona, no Undertale, etc), so it's a huge blow to people who have a wide variety of tastes and a massive library of music to listen to. All of the music they had could have been in the big music streaming platforms like Spotify or you can buy their albums or something to give your playlist a Nintendo flavor but nope, it's tied to this app only because of Nintendo's control. It's useless.
My ideal world has drm-free music where you can pay a fee to access the music files but I know that isn't that feasible outside of small artists.