The grammar-checking service they chose to integrate, LanguageTool Plus, does not have a good reputation, but it is the sort of thing that should be added to an app such as Ulysses
I believe most writers consider Scrivener, which costs $45 for a license (no subscription), to be a better writing app. Ulysses mainly gained momentum because they had an iOS version during a long period when Scrivener did not.
I would be curious to know if Ulysses has improved enough to overtake Scrivener.
You can take Ulysses for a spin and find out for yourself. We offer a fully functional 14-day trial which can be canceled anytime up to 24 hours before the trial period expires.