Far better at catching some types of mistakes. Word only has this many hardcoded rules past the basic grammar. LLMs operate on semantics, and pick up on errors like "the sentence is grammatically correct, but uses an obviously wrong term, given the context".
That's not the kind of thing I'd trust to a language model: I'd expect it to persuade me to change something correct to something incorrect more often than it catches a genuine error. But ymmv, I suppose.
I have definitely seen Grammarly make suggestions that are actually wrong, but I think it's generally pretty ok, and it does seem to make fewer mistakes than I normally do.
Sometimes I use incorrect grammar on purpose for rhetorical purposes, but usually I want the obvious mistakes to be cleaned up. I don't listen to it for any of its stylistic changes.
I've had good results with doing similar. My spelling and grammar have always been a challenge and, even when I put the effort into checking something, I get blind to things like repeating words or phases when I try to restructure sentences.
I sometimes also ask for justification of why I should change something which I hope, longer term, rubs off and helps me improve on my own.
