Swede,
Having had both sensorless (no encoder) and vector drives (with encoder feedback) on a cnc knee mill, I can say I really like the vector drive (might be a Baldor trademark name). It has excellent and accurate speed control and lots of torque for tapping, without having to shift gears. But, of course for cnc, a person really needs to know that the machine can maintain an accurate spindle speed in order to calculate the correct feedrate for tapping. On a plain manual mill, this would not be a requirement, because you would be feeding the quill down by hand, I suppose.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)