On my original slide milling I bought a second slide and had it milled with the CZC plate system, the reasoning is my optic choice may change as new stuff comes out. Once receiving it the quality was so good that on the next one It would be mill the original slide. When I had the S2 milled I used the CZC plate system, added the rear sight plate and good to go. I do not think this will effect my resale (if I ever sell it).
I did hold out with the P10 for the optics ready version and it is nice, and would not regret the S2 optics ready if I buy one.