The accuracy and repeatability of a machine is determined by the sum of all its components, and the sum of all the errors introduced by each component, so besides the ways, other critical areas are the lead screws, the number of steps per revolution your motors/software and electronics can support and the overall rigidity of the machine.
Mintech, ModelMaster and Revos are more accurate because they all use ball screws, linear ways and microstepping systems, they are less common because they are more expensive.
It's certainly possible to get the less expensive benchtop mills out there to a level of accuracy perfectly acceptable for most milling jobs, but you need precision components to build a precision machine.
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