What's great
I initially found Brain.fm on ProductHunt when they launched in 2014. The app(only available as a web app at the time for Android) was invaluable to me for both sleep and focus, so when it was offered, I bought a lifetime membership. That may have been a risky purchase because, at the time, the product was young and an app wasn't even available for my phone yet (!!!), but it was the BEST $150 I've ever spent! I love this app and highly recommend it!
What needs improvement
I love the app, and have my go-to tracks. I suppose, if anything, I would ask for slightly more variety in the deep sleep category. That said, after using this for 11 years, it works like a charm!
vs Alternatives
At the time, there wasn't really something like this aside from listening to sleep music on YouTube (that I recall). I chose Brain.fm because of the deep science behind it and the founders' background. Also, I immediately converted to a lifetime subscription after my trial. It simply WORKED.
How quickly did you feel focus improvements using Brain.fm?
Instantly.
Is there enough variety across focus, relax, and sleep modes?
This was my only piece of feedback, more diversity would be helpful in sleep mode.
Do sessions adapt well to different times of day?
Yes.