This book has obviously suffered by being in 'competition' with Ben Macintyre's bestseller on the same subject. It bears signs of having been rushed out (I found several misprints and minor errors). It is however a scholarly study and delves in to some different areas of research from Macintyre, but in similar depth. When introducing a new character to the story, Smyth, like Macintyre, includes a couple of pages on his background, but typically these will relate to his military achievements and position in history; Macintyre tells you instead about his personality, family, and colourful habits, which is much more readable. On the other hand Smyth goes into more detail than Macintyre about the relationship of Mincemeat to other deceptions and plans and describes better how it fits into the overall strategy of this phase of the war.
The book has an excellent index, but is disfigured by dozens of annoying endnotes. Why authors expect you to turn back and forth to read endnotes is beyond my understanding.
If you have already read Macintyre's book, you do not need to buy this one unless you are obsessively interested in the Mincemeat story, or unless, like me, you are related one of the characters involved in it.