I can’t speak to the content of these specific books, but Packt isn’t always the highest quality. They aren’t as reliable as publishers like O’Reilly, No Starch, or Manning. Humble Bundle is the way to go if you want to try them out though.

Yeah it’s a react native app so it should end up being cross platform. I’m replying from the iOS version and it’s pretty good already for being in such an early state.