Hiya, I bought the book and it is very interesting - all makes sense - but making the actual changes, well that is a different story!! I get their weekly emails as well which are helpful little motivations to keep you thinking about things. I also think about buying the 12 week program but haven't as yet, your head definitely has to be in the right place, and I think it might be unrealistic that you could change long-standing habits that quickly - I guess it all depends on your level of emotional damage and your strength of character.
I'm also from NI. Are you following a specific diet? I'm on Slimming World 5 weeks.