I've discussed this book with my DD's, my youngest is 17.
It's an abusive relationship, she isn't submissive, she's deluded, he is coercing her, which isn't part of a true Sub/Dom lifestyle, more forced sex.
We've always used Hollyoaks etc to discuss abusive behaviour and are an open sexually family, though.
Education around relationships should of starred earlier, tbh.
Strictly speaking, I don't think it does under 18-20, to experience Dominant sex, any good.
If rather my 17 year old didn't read it, but I suppose it depends on the emotional maturity etc.
I would also like an age restriction on young women doing certain types of Submission Porn, as well.
Speaking as someone who is into the lifestyle.