It made me deal with my hatred, intolerance, and lack of compassion. I went through so many ups and downs, depressions and spiritual-like destruction. So I stopped. No psychic powers. Nothing of the sort. But this is not to say it is not effective or an evil mantra, but a very powerful mantra that will open up your spiritual heart to live a life with more compassion, help you realize your weaknesses, or lead you down a path into the dark night of the soul (which can last a very long time).
To simplify, The Great Mani Mantra opened up my perceptions of compassion, service, emptiness, mysticism, and magic and how honest I am with myself and the universe around me. If you are not willing, truly willing, to act upon compassion, leave this for those that serve whether they are honest spiritual counselors or perform works of charity, at least from what I have experienced.