So, it is perfectly correct, that author of this article is talking about mindfulness in regards with imaginary threats and that is very useless for me, as that type of threats actually does not make me stressed out, but inability to save close relative from death I can't perceive as imaginary threat, but it is (pardon my french) sh!t advice to suggest mindfulness in extreme cases(that require most help on anxieties), for example - for someone who would be freaking out over someone close who has died in car accident. The first step would be getting away from that place and not sing kumbaya on that spot.
Knowing that humans have evolved as most violent primates(with everyday aggression amongst themselves), I don't think that meditation is that good, compared to inability to release frustration and anger - from my experience I got a break after I had to deal with situations that required violent solution, so I realized, that for me it had better therapeutical effect and more properly wired to my brains, than "coping" with stress and staying alive and healthy by inability to do anything and trying to meditate.
Learning that you can calm your body down separately from wanting to think about the actual issue at hand is a good lesson.
How many teachers actually have this, and how can one know that the one you’ve chosen is one of them?
In any event, the common wisdom is "you'll know." Or to put it plainly, do you like the person and feel like they have something to teach you?
I like the term "spiritual friend," because it's easy to understand the dynamic by analogy. How do you know one of your friends is truly your friend?
As for how many there are: I don't know. I live in the Bay Area, where the concentration of practitioners is perhaps highest in the US, and I'm aware of maybe a handful of teachers I would consider consider studying with. I'm aware of many more I would not.
It has more to do with the "student".
Meditation—and even just mindfulness meditation—is a domain of practice as broad as "exercise."
If you are interested in engaging with this type of practice, I recommend working with a qualified teacher in a spiritual tradition. These practitioners will have extensive training (at least decades) and will be drawing from a few thousand years of careful study of the effects of meditation (as found in Buddhist and Yogic/Hindu documents and oral traditions).
For working on emotional issues without dedicating years to practice, therapeutic modalities developed in the West are faster, more reliable, and safer.