I started doing this type of meditation in April, so it has been just about 4 months. For the first few months, I did it every day — and mostly twice per day. I found that when I do it twice per day, the major benefit is that I am not exhausted by the day’s end as I used to be, and I’m calmer, and able to be a bit more present because I’m calmer.
I haven’t heard stories about people having episodes of worsened mental health as a result of Vedic or Transcendental Meditation, so I can’t speak to that. But what I can say is that I believe that Vedic Meditation is safe and simple. For me, that is why it’s so effective. I don’t think that it needs to be learned in a special setting to be effective. I learned it in a hotel room on a business trip, and I have been able to do it on planes before (and during) takeoff, in my car (not behind the wheel, of course), in a desk chair, and various other settings.
I hope this answers your questions.