The following links provide broad overviews of "3-person embryos" - the technology, safety and efficacy, and social and ethical considerations. The five resources vary considerably in tone and content.
The following links to a pdf, which includes a summary of national policies on inheritable genetic modification. It is from a testimony given at the House Foreign Affairs Committee Subcommittee on Terrorism, Nonproliferation and Trade by former executive director of CGS, Richard Hayes, Ph.D.
The following two links provide background information on ooplasmic transfer (also called cytoplasmic transfer,) a similar technique to "mitochondrial replacement," attempted for the purpose of treating infertility, that was stopped by the FDA in 2001 due to various problems and concerns.