Trans-fi Audio rim drive motor vs VPI with SDS

I am considering using the Transfi Audio rim-drive (TFARD)motor and speed controller over my 600 rpm motor and SDS. My concern is the speed control/voltage regulator: the SDS makes its own constant and stable voltage. This eliminates speed variation.

Does the TFARD perform the same function or do I need to acquire a voltage regulator?

Thank you for any help?