If you have to go with R-Pro, look for the max weight yellows. They are buttery, flat and stiff. Also much more durable than the floppy ones. I keep two Pro Pigs in the bag now that they released a bunch more, but for awhile I had one stiff yellow RPro and my trusty white Ace Pig. The yellow one held up and was still overstable, even after much beating. Using a floppy one, which I had for awhile, I had several chainouts during ace runs, but that was more from my angle and the speed in which it hit the chains.
I gave a floppy one to a begginer buddy of mine who didn't have a putter and it seemed to work fine for him. I wouldn't say that the RPro (floppy type) is pure garbage, but they will wear out fast and you'd probably need 4 or 5 of them to 1 pro. So really, its more economical to fork out some dough for Pro.
But Marshall Street, Disc Golf Center and a few others still have Pro Pigs in stock at regular price.