There are some similarities and parts interchangeability, but ergonomically there are some distinct differences. S2 is of course heavier, and the balance feels much more forward. The slide also feels quite light when cycling. The S2's grip has an extra angle on the back which gets your grip up high but it naturally points a bit higher than the SP-01, so there's more front-to-back size in the grip. As for trigger, it is lighter and smoother than an SP-01's, but the DA stroke/reach feels a bit longer, and the SA breaks farther back.
The SP-01 has a rougher/stiffer trigger out of the box, but I think a lot of people would find the pistol fits their hand a little better than the S2. Like the classic Hi-Power, it fits a lot of hands just right. You can get it customized/tuned to feel as smooth and light as the S2 or even more if you want.
