I have used Brain.fm for a couple of years now and recommend it to others. I can't comment on the scientific claims because that is not one of my areas of expertise. However, I CAN tell you that when I need to really focus on a project, I always turn it on (with headphones only, as that is the way it is supposed to be experienced) and it allows me to get into 'the zone' very quickly, and I find that I can stay in the zone for long periods of time. It does help that there are several 'genres' of focus music (I tend to use classical, electronic music and piano focus the most).
I have not used it much for relaxation or sleep, only focus.
(I am not employed or otherwise associated with Brain.fm, just a satisfied user)