On large screens open book link will display book embedded in the page. On smaller devices “open book in new tab” button will open pdf in a new tab, because iOS Safari is limited with embedded pdf, with this button book is going to be opened in a separate tab where you can either download it to your device or read it from browser.
Better fluid interface, exploring authors and tags is faster and easier, standard pdf formats that’s compatible with all devices, real-time dynamic search with full text search (misspelling is fine). Potentially expanding database to free public domain audiobooks and non project Gutenberg ebooks in future.