Is the KIRON 28mm 2.0 soft wide-open?

That's what the reviews say. It sure is cheaper than the 28mm 2.0 Nikkor.

I use the 28/1.8G AF Nikkor for almost all my 35mm work. That one is NOT soft wide open. I don't have the other lenses to compare, but a popular internet website gives the following information:
(28/1.8G: The corners are sharp, even at f/1.8. --KR)
(28/2.0: Even though f/2 is slightly softer in the corners, this Nikkor is far better than the Kiron 28mm f/2 at f/2 in the corners. --KR)