Daniel Haqiqatjou undertakes one of the most comprehensive and substantive reviews of this organisation here.
The conclusion is that "much of Yaqeen’s content contains significant errors as well as blatant misrepresentations of Islam and the Islamic tradition. Furthermore, numerous essays advance views that are contrary to Islamic principles and values. Some of their material can even rightly be described as blasphemous."
Due to all this, he questions Yaqeen as a reliable source of Islamic teaching, finding its content potentially creating major doubts in Islam and entrenching incorrect and ideological beliefs in the minds and hearts of their readers.