FWIW, my W read Too Good To Leave, Too Bad To Stay while in the middle of her MLC. (I only know this because I found it tucked under the bed in the spare room.)
I read it too, on the sly, and I actually took a lot of hope from it. First, I saw that it represented some doubt in her mind - which was way different from the "I'm done and nothing's going to change things" face that she was putting on at the time. Second, I tried to read the book as if I were her, and found a lot of the sections were answered with "Most people in your position who stuck it out, were glad that they did so." FWIW!
The two books that she read which I think were really helpful were 5LL and Passionate Marriage. Not sure if she finished the second (it's NOT a light read) but she did acknowledge that there was a lot of truth in what it said about how things go "off the tracks". Again, FWIW!
Thread #10 22 year M, MLC, Piecing since 1/07 Goal: Live with confidence & enthusiasm!