Mantras are only endowed with transformative power if provided in initiation (dīkṣa) with the mouth of a guru. It's not necessarily so much right pronunciation, but fairly the ability with which the mantra is endowed that provides it transforming capability. Vishishtadvaita Vishishtadvaita is one of the key branches of Vedanta, https://sweet-directory.com/listings13287894/the-bhairav-diaries