This is a really silly article. First, it doesn't say Sinn is a bad teacher.
In fact I will say this – If I were to choose 3 teachers who are the best at teaching the basics of technical game it would be DJ Fuji – AFC Adam – and Sinn. There aren’t many people on their level. Based on me know how good of a teacher Jon is I would fully endorse him. Based on the feedback I have gotten from numerous students of his I would not endorse certain things – however he is one of the best PUA Instructors of all time.
The article makes two accusations
1) Sinn is an asshole who picks fights with his friends.
Yeah, no shit. Read his blog. He does not really hide this.
2) Sinn steals material
Sinn credits people left and right. He always said he created breakthrough comfort with Future by working with him to break down what Future naturally does that leads to women becoming intensely attached to him. He credits AFC Adam and Brad P for changing his game all the time. He credits CJ for teaching him same night lays. He even credits people he clearly doesn't like such as Mystery and Style. Actually, for all of his trash talking, he is very good about distinguishing between people he doesn't like and people who are bad teachers.