This book is an excellent way to dive in to Scala for application development, even though at this point it is more of a refresher than an introduction for me personally.
I started using Scala at a new job in 2014 with no prior Java/JVM experience. I bought Functional Programming in Scala, followed by Programming in Scala. FPiS was completely the wrong choice for getting up to speed in my new role, though it was academically interesting. Programming in Scala was closer to what I needed although it didn't deal with larger ecosystem issues. Hands-On Scala Programming feels like the book I should have started reading the first day I started working in Scala development.
6 years later, I no longer have the new-user perspective on Scala and the JVM ecosystem. Does Hands-On Scala adequately prepare someone for the JVM/Java quirks that leak through into the Scala environment? I can't tell now. I've internalized too much of that knowledge.
Assumed Java knowledge was a rough point for me in the first year or so using Scala. If something goes wrong when you're fetching Maven dependencies in an SBT based project, and you have never used Maven-as-Maven because you never used Java before, you may encounter some baffling error messages and lack the context to understand where you go next to fix it. I also encountered a lot of "Like Java's Foo, but with X" explanations of Scala features that didn't help because I never used Java. In the case of the problem with Maven dependency failures and baffling error messages from SBT, I had to resort to running SBT under strace before I found the root cause.