I am always extremely grateful for my grounding and training in early Buddhism and meditation when I read books on meditation from other traditions, whether Daoist, yogic, or later Buddhist, because compared to early Buddhism, these traditions of meditation are incomplete and also unclear in their explanations of what is basically the path to absorption concentration.
In the Daoist system of "Sitting and Forgetting" presented in this book, the founder Si Ma Cheng Zhen drew A LOT on Buddhist philosophy, especially on the theories of impermanence, craving, attachment and detachment, consciousness, and emptiness, and also on Buddhist meditation techniques including, apparently, as stated in the introduction - on mindfulness-and-insight meditation or "nei-guan". However, there is actually very little of actual insight meditation or nei-guan to be found here. It is mostly general stuff on mindfulness-with-breathing, leading to absorption concentration. However, this simple process is obscured by the usual Daoist mysticism - i.e. a whole load of mystic terminology about e.g. Jing, Qi, Shen, mystery, Dao and even obsessor spirits.
If I had to depend on this text for guidance, I fear I would never have understood the simple path to absorption concentration, much less attain it. I always feel extremely lucky after reading these books, that I avoided the general confusion they wallow about in. This is essentially Buddhist mediation and philosophy grafted onto a Daoist frame, which means, one might as well go back to the early Buddhist original which is clearer and more complete anyway, than study the Daoist imitation of it. Still, Si Ma Chen Zhen's text is an interesting historic document about how Daoist meditation and philosophy had been heavily influenced by Buddhism by the time of the Tang dynasty, so much so that essentially Buddhist insights and methods had become adopted as quintessentially Daoist.