The interface is a little confusing when you write a "perfect" text. I just wrote a few sentences, pressed "Analyze" and nothing at all happened. Pressed it again, nothing again. Maybe include a message like "Sorry, found nothing to nitpick about."
I tried it on some decent-looking HN comments. I am impressed that every "problem" it has found has been plausible, but disappointed that all have been wrong. This checker has one hell of a false positive rate.
No errors / suggestions. I didn't get any feedback that the text has been analyzed and is ok.
(I tried it with the original text and got some suggestions. It's working.)