There are many myths about Vedic mantras, and some truths too. One myth for sure is that one can instantly change one’s situation by saying a mantra. Year after year, those who buy into this myth commit themselves to worship ceremonies (pujas) or to recitation of mantras, or to visualizations of what they desire the mantra to produce.
In the Puranas there is sufficient evidence about the efficacy of mantras but this evidence is based either on myth or on what used to happen but which happens no more.
What we know for sure and what is self-evidence today is that a car remote can open the latches of the door of the vehicle by a sound which is emitted from the remote device. The device emits a mantra digital sound which works. It is not a myth. But if I desire to kill someone who threatens me, I could not do so by saying a sound, as Ashvatthama chanted an incantation to kill the son of Abhimanyu.
I use mantras but only as call-prayers for reaching deities who are supernatural beings in other dimensions. It is not to say a sound which will produce a physical action.
There were occasions in meditation when a deity or yoga guru instructed me to say a particular mantra but it was never for me to acquire something physical. Once on the astral side, I was given a mantra by a yoga guru. He said I should use that manta for causing the mind to ceases imaginations and memory displays. Later a deity gave the same mantra and said that I should project non-contaminated mental energy to a certain mental place while saying the mantra as it kept the mind from imagining and illustrating memories.
In both cases, the mantra worked such that in a short time during meditation, the mind ceases it shenanigans immediately.
Thus my use of mantras is for subtle effects, psychological maneuvers.