Unfortunately i have no experience with real 303s. So i can't give you a faithful answer here. From what i have read and a review or two in magazines i think it
is in the 'top 3' if you will. There's a demo there which you might want to try.
And the development hasn't come to a hault/the developer seems open to suggestions, so if there's stuff to get adressed it most likely will be.
I am glad i bought it, couldn't quite get my head around the more traditional 303 programming style. Esp in respect to slides / accents - with silverbox it feels natural and logical to me.