We've done several traditional 3" double head lap / direct nail Cupa slate jobs in Houston. It's a pretty good slate and have had no problems with the product. Consistent cleaving and no sloughing.
We've never used it with a hook system similar to GAF Truslate; although we have installed a handfull of GAF Truslate jobs.
Believe it or not, the Truslate system has fared pretty well through 2 hurricanes. I don't particularly care fo Truslate and, in the end, it will cost more that a tradtional slate roof but it has worked.