I haven't done it often enough to be 100% certain, but I think it only grants that high score extra ball once, but it does allow you to enter initials for the second time you obviously beat the high score you set to get the extra ball...
Picturing a snake swallowing its own tail about now....
still sounds like a good feature/reward for some hard work. Its really worth it for a home machine, in the field, I'd probably prefer the extra game credit.
