For normal tasks, listening to music just works fine. I wrote this complete post while listening to Birdy, and while I'm writing this post I'm listening to yet another song. It really doesn't distract me in any way that I start of mind wandering about something else.
However, for more focused tasks, like studying I can't stand any distracting sounds. As a Tinnitus sufferer I actually need something that gets rid of the distracting sound that I'm hearing the whole time the moment my mind gets distracted. Talking people or music aren't solutions to this.
This is where SimplyNoise comes into play, it draws attention away from my hearing as it's a completely flat sound to listen to and doesn't irritate me in any way. As I have in-ear phones I can keep the volume lower such that it doesn't damage my ears in any way; and as another result I don't hear talking people, music, laptop fan or any other sound that's around.
You can read through a lot of reviews, or try to find studies. But I doubt if you'll find these in a reasonable time. I would suggest you to just try it and see whether it fits you, it might be required to try the different presets as well as the different volumes but you will eventually get somewhere. It probably doesn't work for everyone though, because some people might react different to these sounds.
Human voice is known to draw your attention, music usually includes frequencies in the vocal range (whether instrumental or not); pure noise on the other hand doesn't make any frequencies stand out.