This is what our customers have said about our puzzlebooks:

"My [young] son and I are happily working our way through the puzzle book.  I did have a look at other Sudoku books in Ottakers today, and realised just how superior your book is to those on display.  The spiral binding is preferable to forcing open a conventionally bound book, the better quality paper allows for erasing pencil entries, and the grading of the puzzles mean that [my son] and I can work at our own levels.  The only improvement I can think of for book 2 would be the inclusion of super difficult puzzles.  
Many thanks for many hours of peace."