The CF/ZDP Caly 3.5 is one of my favorite Spydercos. Here's a few reasons why:
ZDP combined with the Caly edge geometry makes one incredible slicer, maybe one of the best out there.
Seems to stay sharp indefinitely, as long as you don't abuse it.
There's an amazing amount of blade packed into that slim, compact handle.
The knife pretty much disappears in your pocket, especially eith the low profile wire clip.
The CF scales and laminated blade are really elegant and beautiful.
Compared to S30v ZDP will be harder with a bit less toughness. It will stay sharp much longer, take slightly more time to sharpen and be slightly more prone to staining.
If you have large hands you might find the handle a bit cramped. It doesn't bother me as I carry my Caly when I specifically want the smallest possible package with maximum blade length.