I haven't seen any posts on Grammarly in this forum. So here is one.
A few months ago I'd finished a long chapter made up of several scenes and began reading it over to rewrite it as needed. I'd recently seen an ad for Grammarly so decided to give it a try. I got the free basic version and installed it in my copy of Word 7.0.
Normally Grammarly is dormant, only noticeable as a tab at the top of the Word page as a green icon labeled Open Grammarly. Click the icon and the page splits vertically in two. The right pane within the page is about a third as wide as the left side. This pane is for Grammarly's comments, which look about like this: pain – Correct your spelling.
Click on the comment and the cursor shifts to the problem word, which is underlined in red. The comment offers a suggested change, which if you click will make the suggested change. Or you can type in your own suggested change – or ignore the comment.
If you don't open the Grammarly pane Grammarly does continue to work, this time by underlining in red any questionable words or phrases but not displaying any reason why.
I found most suggestions given by Grammarly good but not all. They also acted as distractions if I was composing on the fly. So I kept the Grammarly pane off most of the time, only using Grammarly when I'd finished a goodly chunk of text. That chunk became bigger as I used Grammarly more, until finally I only used it after a chapter-sized chunk.
Grammarly checks common usage as well as grammar. It also checks spelling, though that is superfluous as Word does that as well. It handles common usage fairly well, better (though not much) than my subconscious does.
I found the basic free version of Grammarly useful. But I find some of its suggestions unhelpful. I'm also skeptical of its claims that the advanced paid version gives truly "advanced" advice. What has been your experience?