Everything in my review about the current Times crossword series (
The "Times" Crossword: Bk. 12 (Times Crossword)) applies to this book too. There are two significant differences. On a humdrum level, the paper used in the Jumbo books is better - whiter and tougher than in the other books. More important in crossword terms, the daily Times puzzle never uses multiple entries as a way of squeezing in answers longer than 15 letters. So if you want to see these in a Times puzzle (and good clues for them), the Jumbo is the only place.
Stuff about "brain-bending" and the like in the blurb for the Jumbo books suggests that these puzzles are more difficult than the daily paper ones. As someone who has timed himself on hundreds of each, my impression is that once the bigger grid is taken into account, any extra difficulty is accounted for by three things: finding where to write stuff in a bigger grid, the use of long phrases that you haven't seen before, and possibly a higher average word length, so fewer familiar short words. The clues seem no harder than those in the daily paper puzzles - the setters are the same people, after all.
The bigger grids seem to encourage a few more themes in these puzzles - one of the first ten has several types of bird among the answers, for example.
Retention of the precious fifth star is for the same reason as with the other books - no explanations of clues with the answers.