I think most adapters are better than they used to be but maybe I've been lucky.
I recently picked up a no name Hasselblad to Contax 645 and it works fine including infinity.
Most of the cheap ones I have picked up recently for x/to eos work fine also including focus confirm chip models.
When you think about it, it's not rocket science but I have heard of poor tolerances when these first started popping maybe 8 years ago.
I know this doesn't help much but at least it bumps your thread