The blue/green PBA Inferno is not a UI with a pearl cover (that would be the OI, either the red/black PBA one or the orange/smoke one). It's a UI with a polished cover. It's still a solid resin ball, though.
I think a Radical will have a later, more angular move than the blue/green PBA ball. They will probably handle comparable amounts of oil, since Octane is somewhat stronger than the original Activator. I'm not sure both have a place in a small arsenal, though if you're looking for 8+ balls, it might.
SH