You make a good point. After more reading on this, I change my mind. The slew of problems caused by using namespace directives far outweigh the positives of avoiding the use of prefixes for convenience sake.

Even if there are cases where they can be safely used as you've mentioned, its introduction in the book early on, especially in the examples, seems to be a crutch that could lead to an eventual footgun for beginners like me who are following along. I'll reconsider its use from now on.