Any scope above 10X should have parallax adjustment.
As I understand parallax, it is this. The human eye/brain can only process one focal point at a time. So you really can't see the x-hair and the target clearly at the same time, unless they are focused to the same plane. Adjusting the parallax puts them at the same plane...Now, the corrections are not noticed as easily with lower power optics. That's why the higher power stuff needs AO or SF.
For 300 yards and in, a staight 6 or 2-7X or 3-9X should be plenty sufficient.
