Flat and Disc valves what is the difference?

I just bought supertech's stk flat valves. I have notice the oem valves are disc, what is the difference in performance and Smog in CA?

Need some help guys before i put this in my car.

 

A dished valve is used to reduce weight and lower the chance of valve float. A flat faced valve will enable you to increase the compression a little.

 

double post.