I thought about this topic a little more today and after shooting them side by side, they are really different guns. Yes they are stamped "CZ" and "Shadow" but with the considerably larger grip and considerable weight difference, they are truly different feeling firearms in my opinion.
If a shooter has smallish hands, the SP-01 Shadow would be the way to go. If one has to transition a lot of targets, the S2 has quite a bit more weight to push around. The extra weight does help with the recoil but only slightly in my opinion.
If you don't already have a hopped up Shadow that you are proficient with, the S2 is definitely a great starting point. I just don't know if I'd rush out and buy the S2 if I had it to do over again. Still both are fine pistols. Just very different.