I heard they've had a fact-checking crew of 5 people on it for nearly 2 years.

They obviously feel (or felt) it would be explosive and really wanted to ensure its factuality.

The publisher is Houghton Mifflin Harcourt and unless I'm wrong is far and away the most distuingished house to publish the truth about Scientology. They're going to be at least as careful as the New Yorker was.