I switched from carrying a 92FS to a PX4 9mm.
The CX4 breaks down the upper from the lower by a single pin.
My 9mm CX4 uses 92 series magazines.
My 40cal uses PX4 series magazines.
If I take the upper with the 9mm barrel and put it on the PX4 series lower that came with a 40cal barrel, I could use my 9mm PX4 magazines with the 9mm upper. I could also use 96 series magazines in the 40 caliber upper.
Basically beretta makes a kit that you can swap a CX4 from 92 to PX4 magazines by replacing the magazine well and the magazine release which would cost about $50. If I can just push a pin on one and swap it to the other, thats cheaper and easier and a lot more versatile.