Both the PT 24/7 Pro I owned (could not get used to the ribbed-rubber grip) and the PT145 Millennium Pro I just bought have the same lock work: Cycle the slide and its in single action, pull the trigger without the slide cycling and it reverts to double action until the slide is cycled.
The 24/7 Pro is SA/DA, however not all of the Millennium Pro's are. The 2nd Generations of the Mil Pro are DAO. The 3rd Gen of the Mil Pro is SA/DA. The most easily identifable indication of the models are the dovetail Heine Sights. All of the 24/7 Pro's are dovetail sights and SA/DA. The 2nd Gen Mil Pro's have the screw on sights, the 3rd Gen have the dovetail sights. Hope this helps.