On the other hand, where the language gets promoted, I haven't seen anyone really promote C in a way that would sound modern in any sense, where people who have years of experience with C stick with C89 or use C99 in a C++ compatible fashion (i.e. without any C99 syntax which C++ has not adopted officially like restrict keyword or designated initializers). While that is fine for personal preferences, I think it does a disservice to people who have to learn the language and use the language for various justified reasons of their own and there isn't a unified response in how to really teach C to them.
I think the author really hits the hammer on the head with this part in the introduction.
"In contrast to the ubiquitous presence of C programs and systems, good knowledge of and about C is much more scarce. Even experienced C programmers often appear to be stuck in some degree of self-inflicted ignorance about the modern evolution of the C language. A likely reason for this is that C is seen as an "easy to learn" language, allowing a programmer with little experience to quickly write or copy snippets of code that at least appear to do what it’s supposed to. In a way, C fails to motivate its users to climb to higher levels of knowledge."
But on this book, from what I have read from past revisions, it's very well written and I have even learned some things from it I didn't know existed in C, like using the keyword static in array indices in parameter declarations. While it is not a perfect resource and I don't think anyone new to programming would be able to read this without guidance, it does some things extraordinarily well which I haven't really seen other C books touch on. Its treatment of undefined behavior is top notch and the way that it tries to explain the memory model of C is pretty good as well.
But had this book been written for another "antique" language, like Modern Fotran or Modern Cobol (which both had their last ISO standards most recently in 2008 and 2014 respectively, mind you), I doubt there would be this much polarization in the comments section.