how is this one better than their 30mm 1.4 that sells for half the price? It fits full frame?

http://www.amazon.com/Sigma-30mm-Canon-Digital-Cameras/dp/B0007U0GZM/ref=sr_1_1?s=electronics&ie=UTF8&qid=1387230877&sr=1-1&keywords=30mm+1.4