I wish they advertised it more! That reduction in annular pad plus the inner player geometry is a game changer. Effectively any 0.8mm pitch bga is completely prototype-able now.
But if you want signals in those inner balls... still pretty tight. And the 15x15 ECP5 is the absolute max this would work for; after that you hit both needing inner layers to route on, and additional ground planes for the outer layers' return current.