Was reading some commentary on one of the links, close range and no body armor, this would ruin someones day. But the aerodynamics aren't like that of hp (black talon or hydra-shok, if the latter is the proper ball I'm thinking of). My guess is that once the ball penetrates something, the majority of the force is going to drop off considerably. Yeah, there will still be a little umph behind the center slug but I think the vast majority of the damage in the wound channel there, would be due to the number of rpm's it's turning over. Pure copper is fairly soft, so it has to be some sort of copper alloy, and I'm thinking that there is a bit of a limit on the caliber this type of projectile, as the pressure exerted on the front cavity would cause the petals to break apart in mid flight.
While I certainly don't want to get hit by one, I think the jury is still out on how effective these things really are.