1. RF VF prism is better glued and mirror is more resistant if it splits
2. 0.72 mag can take 28mm lenses easily although there are no frames for such length.
3. Frame counter totally brass, easier and more resistant than the glass loup of the m3
4. The quality of manufacture is top notch but solutions inside are better designed after the experience of the m3. For instance there is a sprocket inside that transmit lever force into the mecanism, in the m2 that sprocket has a coil that helps to damp sudden force into the advance mechanism. And if jammed you can simply push the sprocket up and the whoile mech gets freed.
To me the m2 is the best of all Mīs. Second is the M5