I had a pair or two of the X series, and it seemed like the spring in the cleat would bind up much more easily than the flat version in the Zeros. I was always lubricating it or fiddling around with screw tightness.

With the Zero cleats, unless I go walking in mud or something, I never mess with them.

I have wondered about their cross-compatibility; the locked-in "groove" appears to be the same. The Zero has the little depressions in the pedal surface at 45 degree angles, my guess would be that these are to give you some "feel" to the unclipping process by forcing the spring to ride up these depressions as you rotate your foot. If they unclip OK, I don't think you'd hurt anything doing some mix'n'match..or you could home modify your X pedals with a dremel tool.