Hi, I'm one of the authors. "Unsafe" has a very specific meaning in our book -- it doesn't refer to security or to the fact to a feature is inherently bad. It

Hi, I'm one of the authors. "Unsafe" has a very specific meaning in our book -- it doesn't refer to security or to the fact to a feature is inherently bad. It means that the cost/reward ratio of teaching a certain feature and using it in a large codebase to which multiple engineers contribute to tends to be negative. There's nothing inherently bad about 'final', but it's easy to overuse it for no real benefit, and it can cause reusability issues in larger companies where inter-team refactorings cannot be done automatically. That's pretty much it. There are also some excellent use cases for 'final' described in the book, but they are very niche. Hence the "unsafe" categorization, i.e. I wouldn't teach this feature to a new hire :)