Never heard of an NZ slide stop cracking, but cast CZ's break with annoying regularity.
I know of 2 CZ-85s with @1k rounds both broke the same week.
The local range stocks slide stops for it's range guns because they experience it so often.
It would seem to be a design flaw as I've also seen Swiss, Israeli & Italian CZ75/85 clones with broken slide stops.
Having said that, my gunsmith recommends use of a Browning High Power mainspring in CZs (it's a little heavier than the factory CZ mainspring).