A cloud reader it's like a browser, you must be connected to the internet
Use it.
Use the kindle reader or other reader APPLICATION program and download the complete book to your pc or book table reader
E books are about the same size as a medium resolution image, hundreds of page of text will fit in less than a mega bye of data file
I have hundreds of books on my Motorola zoom tablet, you could put a thousand books on your pc and not miss the used space
This way the book is always ready when you want to read, you don't need the cloud and an web connection
I use a called AllReader on my tablet I also have the kindle reader app, but don't use it too much