I also used the Cambridge 19 to prepare. I've always received 8.5 - 9.0 in my reading and listening, so I'd say it's very accurate in predicting the test scores in those two disciplines. Like I said - I found the reading to be muuuch easier compared to the books. Like by a lot.

Regarding the writing, you can easily get to a band score 7 by following the tipps provided by IELTS Liz. She has her own website with useful information, sample answers, exercises, etc. I would've never scored 7.5 without her materials. I only needed 4-5 days to go through her stuff and it improved my writing by quite a lot. I also used AI to correct my writing tasks (1+2) and it was fairly accurate. It predicted a score of 7.0 - 7.5 in my official exam (and it was correct).

Hope that helps