I have a CPA-2 that I've been using for almost 20 years now, have never used a CPP-2. I use it solely for developing B&W sheet film, in Expert drums. (I did a brief stab at roll film early on, but strongly disliked the Jobo reels and found that my established method of Paterson reels in open tanks was less hassle and gave me cleaner and more consistent results.)
My darkroom can get down to upper 50s in the winter, so it's handy to have the heating function. The heater does a decent job keeping a reasonable working temperature in the water bath against a lower room temperature, but it's not what I'd call a high-precision device. You can't calibrate the settings on the control dial and expect to get exactly the same temperature every time at a given setting, you need to keep checking the thermometer and tweaking. Also, I'd estimate that the temperature drift as the heater cycles in and out can be as much as a degree. It's more than adequate for the film/developer combinations I use, and I don't feel any need to upgrade. But if you're doing processes that require tight control within a fraction of a degree, the CPP-2 might be a better bet.
I also strongly endorse getting one with a late serial number.