My specific specimen is branded 'Walimex Pro', but it is a lens of the Samyang family which are being sold under several different brandnames (i.e. Rokinon, Vivatar, Walimex Pro, Bower).
This short demo footage was shot on a 550D using the Lightform C color profile. Even though the general picture looks quite ok, the 550D is really messing up the actual quality of the lens. It's just too sharp for the 550D when there are lot of details, this becomes all too apparent with the shot at 0m50s. The camera and its codec just don't seem to know how to cope with it.
I bought this lens with the intention of mounting it on a Blackmagic Design Pocket Cinema Camera - which should be abled to deal a lot better with these issues. At least as far as its codec(s) go(es).