When I first took a furtive look through Schnell's 30 Years a Watchtower Slave, I wasn't that impressed with it. He seemed to make a lot of claims, but offered very little in the way of evidence.
Those in the "territory" who cited Schnell's work all seemed to have that wild-eyed fanatical look about them, and that, too, seemed to be the tone of the book. It came over as being written by an extremely bitter ex-member who just wanted to "vent his spleen", as the saying goes.
Part of this could well be the more forthright manner of speaking that is common in eastern Europe, but still, I was never left with the impression that here was a great work of literature!