Yes they do work provided they are done with full faith and properly. If you do Mantra ucharan and your mind is thinking about the movie running on Tv than that will not work. If the Gemstone you wear is not genuine then it will not work. Honestly there is so much of cheating these days that you do not know whom to believe or not.
Do the mantras yourself and with full sincerity and you will see the good results.