i was just looking at Seyberts, and they have both the red circle and the super pro (non-measle) for around 16 bucks, not much difference in price...
what is the difference between the two balls?
They are made from different resins.
The Super Pros are a matched set so the ball that comes with the Super Pro set (the red logo ball) is made of the same resin as the rest of the set - the Aramith Super Pro resin.
The red circle ball is made from the Super Aramith resin. I'm not sure but I think this is between the Premium and Premier lines. That would make the red circle ball a lower quality ball than the red logo, by a couple of levels.