There are SIX new Birds of Prey items on the site today. They are the eBooks in what we call Story Pack format. A story pack combines all the background, scenarios, ADCs, MDCs and SOAR aircraft for a given product in a given era. Each product (Air Combat in the Jet Age, Airborne Alert and Fighter Sweep) has two Era-based story packs, one for the "Early Era" (1950s - 1970s) and one for the "Modern Era" (1970s-2000s or similar).
The Story Packs are intended for customers new to Birds of Prey, who have a historical interest in an era, or a particular family of jets. It gives a lower price of entry to get in and explore. Maybe this customer might just read... or maybe they'll buy a rulebook and push around some box-minis to get a feel for how the game works, or how different jets perform under different circumstances.
If you've already purchased the PDFs matching the print products, there's nothing new in them for you, and they're the same price as buying those PDFs. They're just organized a bit differently.
If you have a friend who's interested in the history of fighting jets, this may be a great recommendation!