Both the PGP-ADJ and the PGP-Ultra are high-quality rotors manufactured by Hunter. The simplest explanation is that the PGP-ADJ is a basic model and may lack many core features. However, the PGP Ultra is a more advanced version of this model that has more nozzle compatibility options and a stainless steel riser, along with other advanced features. To learn more about these rotors, our customers can watch our Sprinkler School videos online for free.