VFD

Sensorless Vector control is a little more sophisticated than the V/Hz output of a basic drive, but unless you think you need more precise velocity control I don't think it makes much difference on a manual lathe. Might have some benefit on lower rpm torque but I can't say for sure. I'm much more familiar with tuning Servo drives than the open loop VFDs. Wouldn't hurt to have in your back pocket if the price difference isn't too big.

Sensorless Vector Control of AC Drives