When evaluating a mini milling machine, you must prioritize the spindle motor power (typically ranging from 150W to 1000W) and the spindle speed range, as these determine the materials you can process. Look for machines with brushless DC motors for quieter operation and higher torque at low speeds. Additionally, check the X-Y-Z axis travel distance to ensure it fits your workpiece dimensions, and verify the spindle taper (e.g., MT2, MT3, or R8) for tool compatibility. A solid cast iron base and column are essential to minimize vibration and ensure machining precision.