It's pretty good, but it's annoying.
I'm an aspiring author, and I use Grammarly to help keep my stories free of errors. While it can be useful for this, it is also very irritating at times. The constant pop-ups can be distracting, and the app doesn't understand context, so it will give suggestions that obviously won't work or are pointless. I find myself rejecting 80% of Grammarly's suggestions because of this. Grammarly is useful, but it needs some serious work before it's worth $140/year.