I have the BallStar, and after 5 years of continuous duty, I'm extremely happy with it. FYI, there are two models of the BallStar -- the older model looks like a crockpot (i.e. the controls are mounted directly on the wall of the bucket), while the newer model looks like a blender (i.e. there's a little outcropping control panel at the bottom of the bucket, where the controls face upwards and are more convenient). I have the newer model.
The BallStar has a timed cycle, so you put the balls in, wet the pads with the cleaning/polishing agent, set the timer, and walk away. All of the guts of the BallStar are completely replaceable and parts are readily orderable -- pads, spindle, cleaning/polishing agent reservoir, etc.
Either model of BallStar only does 8 balls at a time, but that is the case with the entry model Diamond ball polisher as well. Unless you can pick the Diamond up at a special discount (e.g. at a trade show), expect the Diamond to be very expensive compared to the BallStar. However, I'd consider the Diamond to be the "Cadillac" of ball cleaners.
Both the BallStar and the Diamond are *extremely* quiet. Speaking of in-operation sound level, that brings us to the Bludworth...
A poolhall near me has the Bludworth, and to be honest, that's probably the loudest device for the game of pool I've ever heard. It sounds like an out-of-balance washing machine full of sneakers on high-speed spin cycle. Everytime the owner fires that thing up, you have to raise your conversation volume level two-fold to hear yourself or to have your partner hear you. A lot of us have to look over to the owner and go, "Really Wayne? You have to do that right now?" However, it does do a good job at cleaning and polishing the balls, and it's been in operation for almost ten years.
Hope this is helpful,
-Sean