The Grammarly Review Summary;
Pricing
It's free, you can't get much better than free. There is a paid for version, and they do remind you quite a bit, but it's not essential.
Ease of USe
With both a plugin and a platform, you shouldn't be short of ways to use Grammarly, and it's easy to see and use.
Functionality
Lots of different issues are picked up, from grammar to spelling, in both their app and platform editor. Doesn't quite work with WordPress though (can you tell?)
Support