You can simply ask the model to point out if there are any problems and then fix them yourself. You don't have to copy and paste its output into your book. You can also pay for an actual copyeditor to edit your book.
You can also edit it yourself and then ask a friend, relative, or colleague to read the parts you are struggling with improving. "Does this sentence flow? Is there a better way to say this? Is this confusing?"
If you're going to sink time into writing a book, it's worth spending some time editing it so your message gets through clearly. But that's just my opinion, your mileage may vary.
You can also edit it yourself and then ask a friend, relative, or colleague to read the parts you are struggling with improving. "Does this sentence flow? Is there a better way to say this? Is this confusing?"
If you're going to sink time into writing a book, it's worth spending some time editing it so your message gets through clearly. But that's just my opinion, your mileage may vary.