Also, this extension generates keywords on the fly, so they don't actually exist in the article and can't be used for relating articles by keywords.
But most importantly, and disappointingly, is that the keywords are not filtered at all! They keywords generated are simply whole sentences from the article. They contain about 5 instances of "the, of, it, is, to, on, etc." It doesn't even filter the word "a". You would achieve the same thing if you simply pasted the first sentence of your article in the keywords.