Originally Posted by bcostin
I have an assortment of cheap something-to-Leica M adapters I bought to use with my Sony A7RII/TechArtPro combo. I've used a few of my Rollei Zeiss and M42 wide-angles on my old faithful M8.2 with good results. (Scale-focus only, of course, since there's no live-view on the M8.)
My adapters range from no-name Chinese eBay varieties to somewhat more expensive brand name, mostly depending on how often I use them and what was available at the time. Fit and finish vary a bit but unless the adapter has moving parts for focus or aperture control there's no practical difference that I've found. Focusing with live-view gives you a lot of flexibility.
Most of the adapters I use are the cheap Chinese variety. But I do not have many "x" to Leica M adapters though these are now becoming much more common. I have in general no problem using the cheaper ones as they are nothing more than a physical method of holding a lens in place and the main constraint is the flange focal distance which can sometimes be slightly out at infinity on some models.
But as you are focusing off the sensor when using mirrorless this is not really an issue most times (unless of course the tolerances are way off.) The better brand I always opt for are K&F Concept adapters. About double the price of the cheapest versions by other makers they are well made with good quality assurance (never had a single problem yet). And are still but a tiny fraction of the price of the big name brands. I have not checked recently but my impression is they are bringing out more "x" to Leica M adapters given the advent of AF adapters for the Sony system which use the Leica M mount.