ZTD is sort of a modified, simplified GTD. The ebook has some excellent points, but it’s not really my style. Some people find GTD unstructured, particularly in the “doing” phase. For those people, ZTD is probably better. Also, ZTD would be good for those who find GTD just a little too much to tackle at once. In ZTD, you phase it in over a period of months, one habit at a time.