A hundred puzzles is about a season of evenings, or one very long journey, or a year of the fifteen minutes before bed.
Six kinds, not one
Packs that are a hundred of the same thing stop being interesting around number thirty. This one runs logic grids, number placement, word grids, sequence puzzles, spatial folding and a set of lateral one-liners, so switching kind is always an option when one type goes stale.
One per page
Deliberate, and it costs paper. Two puzzles per page means seeing half of the next one while working on the first, which spoils it, and it means you cannot hand one to somebody else while you keep working.
Answers in the back
Not on the facing page, not upside down at the bottom. In the back, where you have to make a decision to go and look — which is the difference between checking an answer and being handed one.