And are the books PDFs? Are they legit copies, or scanned from a textbook? If not, why would the publisher let them give it away for free. Just my skeptical mind.
They are in multiple formats including PDF, EPUB, MOBI and online reading. They also include zip-files with all code examples. This is a legit site/service. In the end they try to sell you books ofcourse, these free books are meant to lure you in. But you can still claim a book every day without having to buy anything.