A. The advantages of chanting the OM MANI PADME HUM mantra are similar to the infinite sky. On the basis of how flawlessly trained one’s awareness is and their motivation, even chanting MANI PADME HUM 1 time has the capability to purify heavy negative karma.
For instance, a fully intended monastic who has acknowledged all 4 defeats can totally purify his very weighty negative karma by chanting OM MANI PADME HUM 1 time. So, yes it is truly powerful.