Mmmm, the only difference in the CX4"s is the caliber. They come in 9, 40, & 45. In addition, you can buy the parts to make the gun take mags from various Beretta pistols. It's not hard to do. If you already have a Beretta pistol, buy the CX4 to match it. Keep in mind that the PX4 has a higher standard mag capacity than the others. Also available is a 30 rd 92 9mm mag.There is almost nothing to be done with the 45 capacity. On the 40, you can convert a 92 9mm 30 round mag into a 20 rd .40 mag.
Stay away from those aftermarket ones, especially Pro Mag. nothing but issues, or at least a crap shoot on reliability.