Unless you have a weightlifter's physique, why bother doing a dead lift of the 50+ lbs of a 3 ball roller several times, every day you bowl? Even if you're young and strong, do you bother to lift with your legs, like you're supposed to do, every time you lift that ungainly dead weight in and out of your car/truck? Compressed vertebrae or ruptured discs are nothing to sneeze at.
A 4 ball roller with 2 separate two-ball bags will work fine for the 99% case. A "Joey" added on or a bag that only holds 2 balls can be used for tournaments, when necessary.