I'm not sure if I like this particular plugin, but there are some other tools in this arena that are getting better and better.
FoxType can help you reword your writing, with hints for things like politeness, sentiment, formality, and assertiveness.
Perhaps someday, we'll have tools that handle all of the communication for us. And our tools will talk only to people who also have tools to handle all of their communication. We can build a world of robots that speak to each other, blissfully exchanging polite niceties, because they've learned to do so from watching us.
This sounds disconcerting, but I think there is a sweet spot of creepy utilitarianism in there somewhere. After all, why should I spend three hours on hold with my insurance company, listing to scratchy music punctuated by robotic upsells, when I can have my robot do that instead?