If you had asked this question a few months ago, I would have said that I never use the PS series. Lately, however, I've grown to really like it. Each upper body segment is short enough to tack onto a cardio workout. I tend to use it in a CTX-like rotation. I'll do 45 to 60 minutes of cardio followed by one or two PS upper body segments. I usually only do the standing leg work, though, and skip the floor work (I just don't like floor work in general, no matter what the series).
I'd say go ahead and get PS. I prefer GS, but I'm definitely getting very good use out of PS too.
Shelbygirl