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.
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.