I have mixed feelings about agony books. I'm not a Witness, never was, but I have relatives who are. None of those I know have left, though a grand uncle I never knew did. [He was by all accounts a very disreputable man, and I understand why family more or less disowned him,] I understand that leaving is difficult because it cuts off valued associations, even family. But I don't know that agony books influence the still adherent.
Another issue for me is truthfulness. Some are obviously omitting key elements. I think that's true of the 'historic' books such as Schnell's. We all like to see ourselves as the hero [or anti-hero] of our own life. So we are automatically selective. One of the "I left" narratives I've read is by Charlotte Jennings. My granduncle knew the Jennings family, and though reluctant to tell me about them in great detail, added enough to alter the narrative. And I understand why she would leave out those personal details. So while I read them, they do not influence my personal theology, and many of them - Lloyd's is an example - are repellant.
Do I want them to go away? No. Writing is a way of 'cleansing' the soul, so to speak. If someone needs to do that, forge ahead! From an academic viewpoint, they must be read with caution, and note that they are 'preaching to the choir.' I reject the notion voiced by some academics, that the narratives of former adherents have little to no value. But I've read enough of them to conclude that often the value is very limited, and there are cases of 'false narrative,' where the writer claims to have been a Witness but in reality was not.
I'm rambling, aren't I? It's a family trait. Uncle B has a collection of Russell and Rutherford era opposition books and booklets. He quotes from them in Separate Identity, both published volumes. [You really should read these books. Lulu.com] No balanced history can ignore opposition narratives So, while I see them as "iffy", I would never suggest to anyone to not read them.