Beware: the puzzles in this book are of only "moderate" difficulty. If that's what you want, then this is the book for you.
If like me you enjoy "fiendishly" difficult sudoku (as in The Times - at [...]) then look elsewhere for a challenge. Sure it takes a long time to fill in the samurai grids (5 interlocking sudokus), but the sudokus are not at the "hard" level as it says on the cover. For example, I counted 32 clues in each of the 4 outside grids (by comparison, this would be a "Times" easy sudoku, a Times fiendish has 24-26, difficult is usually 26-28).
Also, unlike most other sudoku books, the puzzles are not graded through the book, they are all more or less the same difficulty.
In short I was extremely disappointed by this book.