On a related note, a posting from my now defunct blog:
"Grammarly Considered Harmful"
Before I wrote this post I checked with DuckDuckGo and found _No Instances_ of the phrase "grammarly considered harmful" on the (searchable) web. I've made that search before and found nothing then, either.
You've probably seen their ads - the thing is supposed to improve your writing - spelling, grammar and style. What they don't tell you is that it doesn't necessarily work well, and that it may be harmful to you or your business' privacy and security.
Some years ago I read a posting from an editor of a website devoted to English grammar where he reported signing up for Grammarly's service and testing it against a number of common grammatical errors. Grammarly failed miserably and the decision was made to reject Grammarly's advertising on that grammar website. Grammarly's efficacy may have improved since then, but to me it seemed like they were using a "fake it until you make it" business model. Whether that's still the case I don't know. They may be using AI and getting better at it.
Quite apart from the issue of efficacy are the privacy and security issues. I recall that in at least one instance someone found what appeared to be a complete transcript of a Grammarly user's data from signup to learning, to substantial use on real business data. Imagine the harm that a rival could do to you if they got hold of _your_ data, or that of your employees. All it takes is one disgruntled Grammarly employee who wants to make some money on the side, and a shady data broker, and your confidential text data is up for sale.
That's assuming that there's no attack from any Black Hats.