Now, I've only used the freebie version so far, but I like what it does. The free version checks for basic things like typos, missing words, and punctuation. It is especially good for the kind of typo that is correctly spelled, but the wrong word.
The biggest downside I've encounter is I can only do 60 pages at a time. For long works, I have to cut it up and upload the bits. That makes it a bit more time-consuming. They promise they're working on it, so we'll see if that changes.
Overall, I'm glad I finally checked it out. I ran a few stories through it, and it located missing words and typos that I, beta readers, and even editors missed. It also flagged when I used British English instead of American English. If you're curious, you can sign up here. (I'll get a small kick back with that link.) If anything, it's worth the free version to catch typos and words our brains skim over because we've read the damn MS a million times and please don't make me read it again!
What about you? Have you tried Grammarly? Is there another program you use to catch those pesky correctly spelled typos or missing words?