Thanks for the great review.
Just a note on the App that "goes with the book".
The Baby Sign Language Basics Flash Card App is just a digital version of our paper flash cards that you can carry around on your phone. Some reviewers complain that they do not show a video of signs in motion. They don't show video because they are simply flash cards, and as such, are simply still photos.
There are some great ASL video apps out there, but the flash cards are a different product. Babies who love the actual cards LOVE our flash card app because it goes everywhere with them on mommy's phone!