I have owned the version I bought this objective and the II a few months after its release. In addition to the significant gain in weight (and space with the new visor), the image quality is virtually unique at all focal lengths (I use it on a 5D Mark III). The sharpness is very good, sometimes too see for portraits. Very nice blur even if we do not get the same bokeh on fixed focal to open at 1.2 or 1.4 is obvious. The autofocus is very efficient. Initially I was a little afraid of the lack of IS, but quite frankly it was never a problem in view of the quality of high sensitivities of Mark III.