Well...I know if I ate some of the things my mother eats (major IF), I'd be in pain/D city. Also, I know in order for it to be successful it is necessary to weigh/measure and journal/log. That's my mother's greatest weakness or the root of her lack of progress for oh, a decade.
It's a "points" system versus calorie counting. Ultimately calories versus points are more accurate in "energy accountability." It has the bonus of group support via meetings.
From what I've witnessed, it has a higher "failure" or drop-out rate versus success rate.