It's similar to the comparison between a needle roller bearing and a ball bearing. Rollers larger contact patches than balls, which equates to higher load capacity. The Nook website shows that a 25mm x 5mm roller screw has an 11000lb dynamic load rating, whereas a 25mm x 5mm ballscrew has a 2000 lb rating.
But a bigger contact patch means more friction of course, so it'll limit your top speed. Again, just like how the max RPM of a roller bearing is typically much lower than that of a ball bearing.
Speed won't really matter on a Bridgeport, but neither will load capacity, since the screw is definitely not the weak link on a BP mill. Did you find a pre-owned set of screws? If you're buying new, I'd just stick with ballscrews.