I admit it first: I have not tested gramarly. Why? Because I strongly dislike who ever try to force me doing something. It's irrational as mush as it would be irrational for you to not promote your product, but I heavily dislike the aggressive and self-righteous manner you do your advertising.
I see your advertising almost everywhere, your targetting system may detect me as a perfect client and focused more on me than on the average client but only the first add leave me with a little "why not..."... the hundred following advertising just makes me angry!
And I'm sad to tel that, but all your advertising is crap! Showing your product as so futile and so fake: "interviews" of people who are obiously too delighted to have only looked at the tool, or an other man who is too proud to lie(.?) at his future colleagues about themselves! I don't consider using modern tool as cheating but your adverting sounds like the opposite. Where someone is pretending to be who he isn't so much that he doesn't recognise himself.
And even if if I don't disagree with using tool to enhance my writing/communication, are you really proud of promoting lies and fakes so much? A tool that promise so much without a single clue! That someone that can't recognise his own work sounds right for you? That insisting so much with a jackhammer that "it's free" just to make you forgetfor a moment that nothing is free in our world and not saying how they fool you to may money from what ever they extract about you?