Thanks for purchasing a copy and for the feedback.
The book is not targeted just at advanced devs. As I say in the preface, it's for a little bit of everyone. In these first chapters I'm trying to show things the "CodeIgniter" way when possible. I know that a lot of devs have to deal with shared hosting and don't really have access to SSH to do Composer updates, etc. so I didn't want to force Composer everywhere. Don't worry, though, the last chapter will be all about integrating Composer into your workflow and will be a big one. I plan on really touching the ideas that Composer is one key part that lets you write a PHP application that happens to use CodeIgniter, instead of writing a CodeIgniter application. I feel that distinction really helps when thinking about app structure and converting between framework version (like CI3 - 4) or even over to other frameworks over the lifespan of a running application.
I chose Twig because it's fairly popular, and was easy to integrate for the example. I could have chosen Smarty, but to be honest, I am not a huge Smarty fan and felt it would be more complex to integrate then something like Twig or Plates, from what I recall of my time using it in the past.
Again, thanks for grabbing a copy. I look forward to additional comments as you get further along. The great thing about publishing at LeanPub is that I can easily make revisions and add stuff to existing chapters as needed any time in the future.
