Catherine -
At this level, IMO, you'd be better off buying two machines rather than one with a speed control. On a larger machine the speed control is a handy option.
One of the main differences between the Santha and CocoaTown designs at this size are in the way tension is applied. In the CocoaTown there is a hinged top that is spring loaded to provide the tension. On the Santha you tighten a nut that puts tension on the spring, which makes it adjustable tension. (This is both good and not-as-good). You can adjust the tension (good), but it's difficult to get exactly the same tension each time (which is not-as-good because it makes it difficult to put exactly the same pressure on the stones each time, leading to less-consistent results).
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@DiscoverChoc