I bought this lens mainly to serve as a lightweight, hand-held setup and that was how I tested it - hand-held with pop-up flash =) no fancy flash-gun or ring-flash, just a pop-up flash diffuser. It performed beautifully.
#1 - the boken is very nice and the sharpness is very good.
#2 - my usual "water-droplet test". stepped down slightly to F5, no flash. sharpness is good and bokeh very pleasing.
#3 - because its a small and light setup, it allows me to close-in and respond quickly to any subjects. this JS would have been a little hard to catch if i had to struggle with a mono-pod or tripod.
#4 - it renders colours beautifully. Not much PP done. just the basic tweaking in camera raw.