Safe Stops were the brain child of the late Jim Cirillo. They consisted of a plated full wadcutter with either a "V" slit, a square slit, or a cup point. They were definately available in .357" and most likely .429". A gentleman named Fuzzy Fletcher was working with Jim at one time and producing them on a small scale. He is no longer in this business to my knowledge.
The original intent of the cup point was to avoid sliding off hard targets like the skull, which round nose bullets will do when fired at shallow angles. The slit design was based upon the theory that a hollowpoint bullet will expand and simply become a larger round nose, and therefore, not be as destructive to tissue. The slit design allowed the bullet to split down the middle and provide two large rectangular petals. This would destroy more tissue in theory.
These are designs that I truely miss. My split nose cast bullets aren't quite the same unfortunately.
If you are interested in the theory and history behind the round, and a damn fine read to boot, order a copy of Guns, Bullets, And Gunfights: Lessons And Tales From A Modern-Day Gunfighter by Jim Cirillo. About 9 bucks at amazon.