Phraseology 2 has a similar feature but with highlights instead of dims. Also more than one word class can be selected at once. https://twitter.com/phraseologyapp/status/413825814145556480...
It's one for the lawyers I suppose. As far as I see it the only reason that I would buy writer pro is for the syntax control (and I want it). If an app came out with the feature for less money I would probably buy the cheaper version.
I think it's fair enough that they have attempted to file a patent here. Their business model relies on having no one compete with them on this feature.
That said, I think they could have handled the announcements with a little more grace. Maybe it's just the adrenaline of launching a 4 year long project?