Its a quite nice lens to use on a crop frame cause you can stand much close than using a 50mm only its not as fast as most 50mm but its is one of the faster 28mm lenses. Only con of the lens is that you have to turn the focus ring 270 degrees to go from one end to the other. However I have to say I love the flare of this lens and in combination with Kodachrome picture style it give a look of filming with an old camera which is actually quite nice look or effect.
For more test check link below to test by Lens Bubble who have made excellent test shots of the lens:
Lens Bubble sharpness test of Vivitar 28mm f2
Lens Bubble Vignette en flare test