Its quality is not so much based in its optical brilliance but its…
Price. It is a cheep lens, that also fits on your full frame canon cameras. It is small an unobtrusive it is bright being that it is f2.8 but if you are looking for sharpness, or optical quality, or low chromatic aberration, or low vignetting then dont go for this lens. Even on a crop sensor camera such as the canon 7d or 550D you are getting almost a whole stop worth of Vignetting at the corners.
The central sharpness is not that bad, in a portrait I did with some flash, it was pretty darn sharp but anything away from the centre is a bit of a let down and gets super fuzzy pretty quickly.
The chromatic aberration is a big letdown for this lens causing some serious purple fringing around the high contrast parts of an image. Below are two examples of the aberration in crops of the original photos that you can see in the video.
So my advise is to forget the old idea that prime lenses give better optical quality than their zoom counterparts. the idea that having less bits of glass inside a lens somehow makes it optically superior is bollox. Modern day zoom lenses can easily out do this lens in terms of vignetting, chromatic aberration and sharpness not to mention its speed of auto focus and its noise in autofocusing. But maybe not on price and size if aperture.
However this lens is not totally lost on me. You see it is pretty darn cheep, and its not too bad if you are wanting to use it on a camera for filming reasons. The only thing you have to take into account is not to use autofocus as this is a noisy little lens at focusing.
After this second break ill add links to all the videos i can find on youtube where people have used this lens
This guy agrees about the price
here is some video with some nice music in the background