The main difference between the PRO version and the usual one is the port for the fiber optic cable and the ability to control the aperture wheel located on the front side of the camera.
Sigma 24-70 F2.8 DG DN II (Autofocus only, Manual zoom gear not included, purchase here)
Materials :
Polycarbonate
ABS plastic
Optical glass
Stainless steel
EPDM rubber
O'ring sealed buttons with spring
Key features:
Vacuum Pump System port
Inbuilt leak detection sensor
Interchangeable port system
Synchro cable port
Dual Fiber-Optic port (Sea&Sea type)
Stainless steel mounting plate 1/4" Thread
40m / 130ft Dept rate
The reinforced metallic bottom plate
In order to connect an external strobe with this housing, it will require to use of a Dual 5-Pin Sync Cord (purchase here) or a Single 5-Pin Sync Cord (purchase here), or a Fiber-optic cable (purchase here) with a Flash trigger (purchase here)