The analog 0-10V can be hard to calibrate to match your target speed and can be jerky depending on your hardware setup. The cost is only 30 - 40 USD for the control board and takes 3 or 4 I/O lines to control it.
I do like the RS485 modbus, as you can use it for both commands to the VFD (set target Hz/RPM, ON, OFF) this saves I/O, as well as monitor stats from the VFD (AMPS, Temperature, Diagnostics) The RS484 card might cost you 50 - 100 USD (might find cheap one on eBay for less) They put modbus on the VFDs for a reason: signal to noise ratio
Just my thoughts,
JH
BTW: Your lathe has is looking nice !