It's a great offer for his fans with two small blemishes. First the PDF is not printable because the document is write-protected (that means you cannot copy and paste the text from this book) and secondly every page is watermarked.
The file size is 135 mb and the download took rather long.
I'd say the copyright watermark is more than a small blemish - it's in massive letters at the bottom of every page and is so distracting that it makes the text pretty much unreadable (to me). I downloaded it yesterday but I think I might just delete it.
It's probably the publisher that has forced these restrictions. I've got another book that the author was happy to share but he was upfront about restrictions the publisher put on him. I would say if you enjoy the content then buy the hard copy to reward the author for their work.