Quillbot is extremely useful if you have to summarize chapters, write introductions for blogs, or summarize academic papers on a regular basis. It is not only a grammar checker, so authors can still benefit from it. The only thing we don't recommend is proofreading.
In comparison to Quillbot, Jasper AI is much more expensive, but it delivers superior results. As well as paraphrasing and summarizer tools, it comes with much more. Using Jasper AI, you can compose new text, and it does it very well.
The best proofreading software that we recommend is ProWritingAid, which has most of the features that authors need in a service like Quillbot.