That is true that it is called knitbone and it definitely has stimulating properties to skin cells and bone and was used traditionally as a wound healer. But those same alkaloids that stimulate the proliferation of cells can be damaging to the liver. It's an herb that requires knowledge and extreme caution. It's really not worth the risk in using and if anyone decides to use it, please seek the advice and guidance of an established herbal practitioner. Overall, it is not recommended for internal use and caution advised with external use.

From Mount Sinai:
https://www.mountsinai.org/health-library/herb/comfrey
And information on Barbara O'Neill. She is actually not a naturopath and has no medical credentials. Please read this very informative page on her practices and her subsequent ban by the New South Wales Health Care Complaints Commission.
https://en.wikipedia.org/wiki/Barbara_O%27Neill
Barbara O'Neill (born 28 July 1953[1]) is an Australian alternative health care promoter, known for advertising unsupported health practices described as dangerous by the scientific community.[2][3][1] She presents these claims at alternative medicine organisations, wellness retreats, and Seventh-day Adventist Churches despite not having any recognised qualifications and failing nursing training.[4][5]