I have no qualm with this book, it simply....was not useful to me? I don't think, as far as productivity books go, it was bad — it was actionable, relatively light on padding and pseudoscience (I say relatively but not entirely), and fairly self-aware. It did not promise anything unreasonable.
The two things that I found wanting:
The one most interesting thing the book offered was the relationship between habit and identity, and the performant nature of habits. That made me stop and think for a bit.
Anyway, I did not like it or enjoy it but I think I would still recommend it to people who are like "I have no idea what habits are or where to start". It is a good book for that.