It's a really nice product but the downsides are: 
  
-Oval shape specular hightlights  
shown on this video at 6:22  
https://www.youtube.com/watch?v=tVOhac0FQkw 
(correct me if I'm wrong but even thought in this test it isnt the M4T version, I presume it has the same issue) 
-Slow autofocus (dont care much for video) 
-"Onion ring" bokeh (we can see those on the first image Andrew posted) I find that this very disapointing. 
  
am I missing anything?