I haven’t read it yet, but I don’t think the value of a book is defined on weather the main claim is already known. Knowing that something is good or bad doesn’t undermine the value of a book about it. You can get value by having an additional perspective, understanding the strategy, modus operandi, or the mechanics behind it.

For example, I’m currently reading 'Why We Sleep'. Obviously we all know that sleep is good for health, but reading the book gave me better ways to understand how good it is, analyze my own sleep quality and what I can do to improve it, and very importnat: show me how I can use ti to leverage other parts of life, like learning or emotional regulation. It’s not just “sleep 8 hours a day.”

So I imagine something similar might happen with her book, even if you already know some companies use questionable tactics, it can still be useful to understand those tactics, how companies avoid getting caught, how similar patterns might appear elsewhere, etc. It can also make you reflect on which limits are acceptable or unacceptable, depending on your political views.