Choosing the correct angle is simple. Rather than specifying "right-handed" or "left-handed," which can lead to errors because some right-handed shooters will want to wear their magazine pouch on their right side and some on their left... we've chosen to refer to right-handed or left-handed use.
Left-handed use = you use your weapon with your right hand, so you grip the magazine with your left hand, and whether you place it on the right or left side of your belt, the angle will be correct.
For right-handed use... the cleverest among you will have already figured out that it's actually the opposite.
Quick tip: To know which hand to choose, the right hand is the one where the thumb is on the left when you look at it from above.