If you're looking for a Christmas present for Uncle Fred, who's been solving the Telegraph crossword for decades, or for a younger solver interested in puzzles of the past, this is a good buy.
For each of the siz setters, you get a short biography (roughly 8 pages on average), and twelve puzzles, often including the setter's first and last Telegraph puzzle. The six setters, with periods of setting for the DT, are:
Leonard Sidney Dawes 1925-63
Douglas Barnard 1958-92
Alan Cash 1963-88
Bert Danher 1978-2002
Ruth Crisp 1985-2005
Roger Squires c. 1985- (start date not clear from book)
Val Gilbert has done a good job on the biographies. The puzzles by the last three should be solvable by anyone solving current Telegraph puzzles, and the ones by Barnard and Cash won't be much harder, based on the two I've tackled so far by each setter - though you'll start to see some different expectations about your knowledge. The Dawes puzzles will be much harder - these are from the days when there were no accepted rules about cryptic clues, so you'll see some clues that wouldn't be allowed by any crossword editor today. But by the time you get to the 12th puzzle, No. 10,000 in the series, you'll be doing much better, admittedly with the help of some very easy long answers.
Like the earlier book for the Telegraph crossword's 80th anniversary, the hard covers make it convenient for idle solving on the sofa.
A minor correction of the impression given by the back flap blurb, quoted in the product description above: Val Gilbert retired from editing the Telegraph crossword in 2006, as her introduction indicates perfectly clearly.