Silence is a very poor control indeed! We absolutely test against other music. For internal R&D we've tested against 'focus music' taken from other services, but this is not necessarily something you want to do in an academic paper.
Instead, in a paper we're working on, we take the even more controlled approach of testing music that is exactly the same, except for the addition of particular kinds of processing (this work is in prep for submission).
The question of preference and genre is very important for effectiveness, and people differ enormously. We try to offer a wide enough variety so people can select what works best for them in terms of musical style.
But no matter what the genre, Brain.fm's techniques are applied to make that music more suited to the task at hand.
For example, we do offer a selection of Brain.fm-ified Bach (in the Classical Focus section, under 'more music' in the web app). I love Bach but find it distracting when I'm trying to focus. Brain.fm processing removes some distraction while keeping the stimulating feel of the music.
When I was travelling last year I used the nap / sleep mode a bit and I found it did help if I was finding it hard to sleep.
Of course this is totally subjective so your mileage may vary.
Brain.fm does "work" in that it definitely has helped me focus, but I think one could craft a Spotify playlist manually with some effort in order to achieve a similar effect.
Wish I had thought to listen to sleep mode last night between 3 and 6 AM while I was tossing and turning in bed.
As someone mentioned below, I could put together a Spotify list but why? Brain.fm does the job and I don't need to.
When I need to focus, my two choices are Brain.fm or "Ok, Google. Play some downtempo ambient chill instrumental". The latter oftentimes distracts me. The former doesn't.
I was having some technical difficulties with the site (not the apps) a while back. The head of the company was helping me to debug the problem. Great customer service. Turned out it was something on my end.
I too landed the lifetime subscription.
Highly recommended!
Because I already pay for spotify?