I like this Pocket Sudoku collection because, for one thing, it lists one per page - so it is a decent size! Also because the range is good, 50 at each of level one, two and three difficulty. Each group of 50 finish with a more difficult one that requires diagonals as well as vertical and horizontal completion correct with 1 to 9 range. Number 150 is especially tough! I also like receiving this book in the post as it costs less than the shops and saves searching for it when it may be sold out.