I used it when I was poorly because I wanted to stave off any colds etc. You have to use a certain strength (10+ I seem to remember). It was expensive but a spoonful a day seemed to be enough.
I've heard of medical staff, back in the seventies, using it as a last resort for wounds which refuse to heal. It just tastes like honey so it would be difficult to tell whether it is genuine.
The advice I got is that it comes from a very small area in New Zealand - hence the price - so that's your first clue. I certainly didn't catch any colds or anything like that while I used it, but that's not proof of anything at all. It's worth a try and it's a very interesting research topic if you have the time.
My understanding is that all honey starts off with benefits but most types lose lots of these in the processing which is necessary for health and safety reasons. Manuka manages to hold on to the good things (that might be overly simple but it works for me).