This text is not just a commentary on ngondro, but includes extensive commentary on so many aspects of the path, from conduct towards the Guru, how to listen to a Dharma teaching, etc. etc. that it should not be missed even if one has completed ngondro long ago and doesn't plan to do it again.
Also, just a clarification: this is HH Dudjom Rinpoche's own commentary on the LONG Dudjom Tersar Ngondro.
Often, what we are given in the west by various Dudjom lineage masters is the "concise" Dudjom ngondro to practice. In addition to the concise ngondro, there is the elaborate one, which has different melodies and is longer with much more detail. Obviously, the commentary by HH on the long one will be immeasurably of great benefit also for those practicing the concise one, (just as Thinley Norbu Rinpoche's commentary on the concise ngondro would benefit someone engaged in the long one)--and for anyone practicing any ngondro in general-- but I wanted to clarify because if you look at the chapters you will see the order goes 4 thoughts--> refuge--> vajrasattva --> mandala ---> guru yoga whereas in the concise the mandala offering goes before the vajrasattva accumulation. There are a number of differences also concerning visualization, etc. that should be clarified with one's Lama. I know people that begin with the concise ngondro, and then move onto the long one as a second ngondro..
Contentment is the ultimate wealth;
Detachment is the final happiness. ~Sri Saraha