Where Grammarly fixes sentences, ProWritingAid examines a manuscript. Its reports cover the things that only show up at length: the phrase you have used forty times, chapters where every sentence is the same shape, pacing that sags in the middle, dialogue tags that have become a tic. For anyone working on something book-sized, that view is the difference between polishing prose and actually editing a book.
The volume of feedback is the catch. Run a chapter through every report and you will get more suggestions than any human should act on, so it rewards learning which two or three reports matter for your particular weaknesses and ignoring the rest. Slower and more technical than Grammarly, and considerably more useful past about ten thousand words.