Those might be "2 piece" to save weight but they're not floating rotors.
Here's what true BMW floating rotors look like:
Notice how the rotor ring is separate from the actual hub with pins? The Z43.5is rotors are the same as what came on E60 545i. The hub itself are two piece with aluminum inner hub, but the outside hub and rotor are still attached...
While it does serve to lighten the load, it has little to no performance benefit in comparison to floating rotors wrt heat transfer and management.