Being a learning disabled author, I've found your program better than a professional editor I've worked with. I have four ideas to help your program.
1. I found your grammar checker doesn't notice when I place a comma before that. Commas should usually be removed before a that-clause the only exception I know of is if it is the second word after a name in dialogue.
Using another word other than that might be a better idea.
2. I suggest separate the vague word from the diction report because I had to hunt to locate the vague word report. Vague words would be more useful with a filler word hunter. While all filler words are sticky, not all sticky words are filler.
3. I use text to speech software to proofread, and I would find it useful to be able to use text-to-speech in the app, with the option to purchase voices outright, so writers can send out Beta reads, ARC, for sale, and to disabled readers who prefer Text-to-speech.
4. When I am editing in-app, I would find it helpful if there is a search function. I can't find a magnifying glass in-app.