I tried this out on one of my blog posts, and it classified it as "average", suggesting only single-word corrections that don't even make sense in the context.

A few examples:

It suggested changing "attack" to "defense", in "in order to carry out the attack".

It suggested changing "helpful" to "supportive", in "ifconfig gives helpful statistics".

It suggested changing "grow" to "better", in "expect [a number] to grow continuously".

So while it's a cool idea, I'd say it didn't seem to work very well for me.