Can be confusing as in the states osteopaths have proper medical training too but here it is different. This article summarises. There is insufficient evidence to claim definitively that it works.
http://edzardernst.com/2013/06/osteopathy-based-on-little-more-than-wishful-thinking/
The final paragraph is why I think it is important to question it when it comes up in discussions.
For someone with limited funds it is very likely that they will be better served by going to a physio on the NHS than paying out cash to an osteopath for something that probably will not be any more effective. Or even not work at all.
I feel strongly that anyone asking for money for medical treatment should have proper evidence to back it up.