"Why does he do that?" worth buying?

[CarGirl]

Is it worth buying this for someone who has already managed to successfully leave their controlling/abusive ex?

Absolutely.

Yes. Helps you make sense of what happened.

I found it fairly sound but tbh most of the things in it were obvious to someone with a degree of knowledge about psychology.

I didn't find it sprang any revelations on me.
I would just be supportive, lend her a copy if you have it but ask first, she might not want to dwell on him iyswim.

You sound a very kind friend.

Yes, especially to help you understand why you got there and why you stayed. For the £8 or whatever, it's money well spent IMO.

I am a psychologist by training so understood the concepts, but when it's happened to you it's very hard to be dispassionate and objective. The book also hammers home how the patterns that are so similar across the board and you as the person on the receiving end couldn't have said/done the 'right' thing.