HP-28 series had CAS (first released in 1987), they were replaced by HP-48 series which also had CAS.
RPN was lovely because it was significantly faster to operate with. I remember showing up at math class having just received an HP-48G "because it's what the engineers use" and everyone else just got TI-89s because that's what the teacher had (TI gave teachers free TI-89s and did more marketing). The math teacher hosted an impromptu calculator speed contest and I beat out everyone else by a significant margin.
RPN was lovely because it was significantly faster to operate with. I remember showing up at math class having just received an HP-48G "because it's what the engineers use" and everyone else just got TI-89s because that's what the teacher had (TI gave teachers free TI-89s and did more marketing). The math teacher hosted an impromptu calculator speed contest and I beat out everyone else by a significant margin.