My Take
My overall opinion is that this program is great for teaching grammar in context. And while it teaches rules, it does not do so in a route memorization way, but a more organic way (the way most of us learned our first language).
How I Use It
Setup: You download the extension on your web browser, and the app onto your phone. You can sign in with Google, and then you're off.
Daily Use: Whenever I am typing, Grammarly is quietly in the background assessing my work. It will underline places that it has suggestions about my writing. I can then click the link for the suggestion, and the reason. It has helped me edit misspelled words, as well as taught me additional places that I should be using commas in my writing. If you want to use it to help students advance their vocabulary, it can also make recommendations for that (so instead of a student putting and/and/and all throughout a paper, they can learn some appropriate synonmys in context.