This is not necessarily buddhist, or Theravada, meditation. Goodreads says about the author:
'With more than 140 techniques and practices drawn from Christian, Buddhist, Hindu, Sufi, Taoist, Pagan, Jewish, Native American, and mystical traditions. ..... '
You may be better concentrating on the methods taught by the Buddha initially.
---The trouble is that you think you have time---
---Worry is the Interest, paid in advance, on a debt you may never owe---
---It's not what happens to you in life that is important ~ it's what you do with it ---