actually if I do have one small criticism it's that the flipbook implements 2d6 not very well. Of the 28 pages, 24 pages have a pair of dice printed on them, with the mean being 6.75. Throwing a pair of dice has 36 possible results with a mean of 7.
The probability of rolling 8+ on 2d6 is about 42%, using this flipbook it's 38%. Shouldn't be particularly noticeable over a one-shot session.
If you want to use the flipbook to reference a d66 table, you can flip the book twice and use the second die of each pair (no page has a "2" as the first die, so don't do that). This has a less accurate distribution, but unlike the printed dice pairs can roll any d66 result.
(yes i do get that printing costs of a 28-page booklet are lower than a 40-page one. It's a *small* criticism)