Is this regular old RA-4 process paper that's cheap enough I can experiment and learn?
Absolutely. I find the exposure, filter packs and processing almost identical to endura. I use the exact same processing chems and times as I do for Endura. Can't beat the price for over 700 8X10s. I won two rolls of glossy and one roll of lustre. That's over 2000 8X10s for less than 100 bucks, delivered. With that much paper, I find myself experimenting a lot that I would never do with expensive endura. I cut enough to last for a while, and keep the rest in the freezer. The rolls aren't that big. While I haven't tried it for portraits, (I mainly shoot landscapes) I can't tell much difference from Endura. I find the saturation and contrast more similar to supra than portra.