If you start the app itself, you'll get to choose the spellbook on the very first screen. Pinning spellbooks to the start screen is just for convenience. So, yes, they can be accessed from inside the app.
This is good, I don't want my start menu congested by a bunch of spell books.
Is there a way to use your spell book to create your prepared spells list for the day or track spells per day for spont. casters?
This may be reaching a bit, but it would be nice to be able to go into my spell book and select the spells that I will be preparing that day and have it create a sub list with my selected spells, with a way to track spells prepared multiple times. Maybe even make it able to adjust a spells level to allow for the application of meta magic feats.