Full frame lenses on APS-C left me always smacks of waste, one uses so in the end only 66% of the objective.
The 30mm f / 1.4 is a great alternative for those who are "on budget", but in spite of everything visible weaker than the 35mm f / 1.4 in the imaging performance
Of course, the price is much lower from, but Sigma wanted to go with the Global Vision product series yes no compromises, that we have here, however. Namely, price vs. Quality.
On the other hand you have to see that the lens is easier for it advised also much smaller /.
Personally, I'm not going to keep it, who is the 35mm f / 1.4 but too expensive and / or too heavy, has little alternative to this here. All other 30mm which are worse for APS-C.