It is not a reliable service. The CEO likes to say that it failed 1 time out of 10,000. In Panagrams own research the failure rate was shown at 2%. That's a pretty massive difference.
How about you do this, write your own words on a topic, but use AI-isms in it. A few 'not X but Y' an a few EM dashes and watch it say you're text is AI written.
Writing using AI stylisms has nothing to do if a text is actually written by AI or not. The tests are mostly bullshit because just adding some informalisms in the text corpus tends to get it counted as non-AI. It's not detecting what you think it is.