What stands apart for me is their privacy and security policies. At 10,000 foot view it may look similar to others but when you dig into it, you find they opt you in to auto-deleting data after only 2 months, the keyboard app used on mobile uses encrypted connection back to their servers and does not pass sensitive fields back (there are options clicked by default for username, password, and few other fields to not be passed to grammarly, so they never get sent over in that manner), they do not sell your data, and there are few other good things.

I thought Grammarly would make me lazy. On the contrary. After about one month of use I found that I no longer make mistakes worthy of Grammarly corrections! I do appreciate the automatic typo correction that is not your normal auto-correct.
I was great before and now I am an expert.
Worth EVERY penny.