I haven't found much on how it compares with the Happ trackball, but a couple people said Happ was noticeably better, one guy said he liked his imperial trackball better.
So, I'm thinking about getting a used/refurbed Betson/Imperial 3' trackball. I don't have much money to spend is the only thing. I don't have a cabinet or arcade controls or anything, just want a trackball to play some bowling/golf games/whatever else I can use it for on mame.