Thanks for the advice. I've already used a PS review service catered towards Oxford & Cambridge students, and they gave me the green light; for obvious reasons, I won't put any part of my statement here, but I'll try and describe what I did. I'd talk about a book, give something which ignited interest in the subject, and then elaborate on that, connecting it to my course; when I say "great detail", it's in the context of the character limit. I wouldn't talk about the book's content for more than a sentence; more about how the book impacted/interested me. Since I wrote a PS for joint honours, I spoke about one book which had both applied and theoretical politics (The Case for Democracy), two philosophy books unrelated to politics (The Divine Comedy, & The Idiot; the latter isn't purely philosophical, though I took the philosophical message of the book, being a critique of 19th-century Russia, and went with that), and then two political philosophy books, Lenin Lives & Egypt: The Moment of Change to try and check all the boxes.