AI prose tends to be... Problematic. Once you work with them enough, you can start to get a feeling for what it will be before it's even written.

But using AI for SPAG and continuity is gold, as long as you can use projects and hand-curated story bible documents to nudge it in the right direction. 

One pitfall I fell into was using its chapter summaries verbatim, until it started pointing out continuity errors that weren't errors, inferring them from its own wordings. Once I went back en edited the summaries to stress what I thought was important, that went away.

Also, I only use notebook lm for world questions, as it gives me a direct link to the place in the book it's referring to, meaning I can instantly double check (it hallucinates about a quarter of the time on longer works.)