We're planning on following that one up with a more robust study, because our users do get great results with HRV and it's an interesting topic.
One of our former neuroscientists published a meta-analysis, but it's a bit outdated now re: what we're doing. Still, it's on our site or in the journal if you're interested. :)
On the brain.fm they list results, but they are super flimsy. For focus, for example, n=17, and the difference between music vs non-music is much smaller than the standard deviation of either group.
So it's possible this stuff helps you focus, but it doesn't appear to be showing up on these studies.
It's actually a really good result, for a number of reasons. But I'll let Giovanni respond to this later and clarify (he's the neuroscientist that wrote the paper).
I apologize for the delay, he's dealing with some family and health problems right now. But I promise we'll clear this up.