We have found it useful over the past six years or so. As Jklm posits above, though, it's going to be most useful with kids who are old enough that they have some metacognitive ability to internalize assistance.
We also found that many of the suggestions were not applicable-- but that is not necessarily a failing of the book in my estimation. It's merely that it is a toolbox, and in spite of it containing a hammer, most of our problems in particular called for a screwdriver instead, if that makes sense. For someone else, the screwdriver is not going to be helpful, but the hammer will-- both are present in this book.
I will also say that I find it deliciously ironic that when I went to check this book and one like it (Late, Lost, and Unprepared) out several years later... the latter was not available. Why not?
Well, because someone LOST it... 
As they say, the apple doesn't always fall far from the tree.
I do appreciate that this book doesn't necessarily pathologize executive function in any way-- it simply IS, and the suggestions for scaffolding and other interventions are made upon
no particular assumptions about the need for permanence.
I found the tests extremely accurate for all of our family members. DH is highly sequential, with remarkable auditory recall and executive function (he was, no surprise, a STELLAR student), I am highly visual/spatial with excellent recall in that domain and also have well-developed EF in some domains... and DD is a mixture of us both.
We all have very particular EF/metacognitive blind spots-- and compensatory strengths to manage our way around them-- but this book (along with a couple of others in this same vein) have been helpful to us in hothousing DD to better use her developing compensatory strategies as she matures, and for her to
recognize that being 14 and PG means that she HAS to rely upon scaffolding and consider herself somewhat impaired relative to peers-- but that this impairment is likely to be temporary, since genetically she doesn't have a lot of EF problems in the family.
That makes her more amenable to suggestions that she rely upon supports like using a planner, writing things down, using her smartphone to monitor a calendar and issue alarm-reminders, etc.
