I am about half way through her book and it is interesting. She has done a lot of research and it shows. As to whether it was worth 6M who knows. I don't want to give an opinion until I have finished it though. It is a good read.
I bought it over the summer last year and read through it really quickly. It's a gruesome read, but it'll keep you turning the pages. I definitely found it quite interesting and plausible for the amount of research and damning evidence she found. But, we may never know since the cases were so poorly handled.