Like all different cameras, they are all made differently. The flange distance for diffent M bodies are made differently. Not by accident, but intentionally. No manufacturers will publish this openly and they will not deny outrightly. Reason being that they cannot make a camera exactly the same as the leica M bodies even the copyright of M mount has lapse after 50 years.
Using film, it takes an eye as sharp and skill as good as Erwin Puts to be able to tell the diffrence. Layman like me can only tell whether the person in the picture is a girl or man...
My advise is, if you embrace technology and enjoy the conveniences of auto everything, haxar is nice. But if u are like me, old man like old gears... Then a mechanical body is perfect for me. It's heartening to know that sony still support Hexar. Glad to know that they are not killing their roots even the original technicians probably would have retired or retrenched...