I can see the controversy of designer babies vs. removing preventable genetic diseases to prevent suffering and death becoming a wider-reaching hot button subject since this decision has been reached

As you rightly say, it's only to correct defective mitochondrial DNA and not to allow "designer babies". That whole thing was predicted by Aldous Huxley 80 years ago in his novel Brave New World and, certainly in the UK, it's had a lasting impact. Which is probably why human fertility medicine is so strictly controlled in the UK by a government regulator, and that will include the new technique.

In fact the USA pioneered 3 person IVF back in the 1990s Then Dubya banned it

Seems a no-brainer to me provided it's properly regulated and the science proves it's safe. If we have the science and skills to prevent children suffering from a terrible genetic disease then why wouldn't we want to do that? I just don't understand bible bashers wanting to stop us using human skills to prevent children suffering - why would their God have bothered giving us those skills? And I don't buy the hysteria about children being "psychologically damaged". I believe around 30 children were born using the US technique and they seem to be living "normal lives".