I have the qualification. I can only do about a 2 a day. Of the 20 I've done, I've gotten feedback on about 5 and all of them have been beneficial. "Be careful about writing in future tense", "pay closer attention to the instructions on the headers," or the one from today "be careful about overly wordy sentences that may cause readability problems" and they gave me the sentence, which was way too long. I think they've been dead on each time, to be honest.