I like it.
I think it is more useful for beginners.

An amazing add-on! Greatly improves my spelling and punctuation for several European (though not only) languages. Uses power of open source/croudsourcing.

Excellent application for me as I tend to write very quickly and it catches all my mistakes

Me resolvio cuestiones ortograficas basicas que solemos tener cuando escribimos rapido. De gran ayuda.

Хорошее приложение! Помогает развиваться!

Self editing is tough. If you wrote it, it seems right to you. Finding errors is not easy, but necessary for your words to be taken seriously. This add on can see the small errors in your text that you can't. Their support is excellent as they responded to a request for help at 2am my time. I'm impressed.