Their customer service is prompt and helpful.
However I often have to send them error corrections for things that are not errors. We're talking basic punctuation type things, not contextual or stylistic. Their response is usually "it can't pick up everything." (Paraphrase) the other day it told me that a comma was used incorrectly after a dialogue tag. It read the sentence incorrectly because the dialogue ended with a question mark and closed quotation marks. Grammarly's basic coding should recognize that as one sentence, not two.
I also can't tell it to ignore things like names, or add to a white-list dictionary.
For the most part I LIKE using Grammarly, it has certainly helped keep my grammar and syntax consistent, but I'm glad I got a 50% discount for the first year. I don't think I'm going to renew for the full $140 for a YEAR, but I'm only six months in to my subscription, so if improvements are made I might reconsider it. However a few other applications have been recommended to me, such at ProWritingAid, so I will check them out before I make a decision.