That breathing technique sounds like a form of meditation, so I’d guess it will be quite effective. I really recommend mindfulness meditation for taking back control of an over-active mind. There are tens of books about it on Amazon and it’s easy to get into. Great for improving concentration, neuroplasticity, stress management skills and pretty much anything involving your brain. There are a bunch of studies that support it, including one of the ‘happiest man in the world’, who has over 40,000 hours of meditation experience.