The PDF subscription is a monthly email with a link to PDF files you can print out yourself. The PDFs include full access to the activity book.
The physical box will include all of that in paper form, plus trading cards, a small toy, coupons on toys, and stickers, temporary tattoos, or other fun stuff. Plus, the joy of a surprise in the mail!
We highly recommend the physical Bitsbox. Our testing shows that kids are much more engaged and motivated by real stuff. But it all depends on your child, and you know them best.