Hey Dave,
I bought mine here, but not in the store, but via online shipping. I just notice that they are more expensive today. Buy the EMI filter with matching footprint and the matching braking resistor with it.
these are clickable links which explain it! 
Vector control enables a VFD to achieve extended speed and torque control compared to the more simple scalar voltage/frequency control. In practice, this means more torque at low speeds.
ModBus override means that when you pause your running g-code program on the Onefinity Controller, you can switch ModBus override on, alter the spindle speed on the fly to a value other than it was transmitted by the controller, and resume the program with the spindle running at the altered speed. ModBus override allows also to stop the spindle in case you want to pause your g-code program over night and resume the next day. Both things are not possible with cheap chinese VFDs, because with them when ModBus mode is enabled, manual controls are disabled.