Speed Box for turntable

Bernardwong, I can't speak to the Junior, but I can as to both the VPI 19 MkIII and the VPI Scoutmaster. With either the Walker Audio motor controller or the VPI SDS motor controller, these turntables benefit as follows: the background gets blacker (the silence between the notes), imaging is more stable, and instruments take on a greater solidity and greater apparent dimensionality. The improvements are material and, depending on the resolution ability of the remainder of your system, these improvements either are immediately noticeable or are noticeable after you've lived with the motor controller in place for a week or so and then remove it. However, there may be greater improvements to be gained by upgrading your turntable in other ways before adding a motor controller.
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Have also read about (but have not actually verified myself) that upgrading the AC cord connecting to the SDS results in sonic benefits. It would seem then that upgrading the AC cord wired into the motor would also yield improvement, although that one is hardwired & so isn't nearly as easy to change as an IEC cord would be.

Bernardwong, I have had great results running my HW-19 with the SDS. Given the age of my table I took the approach of upgrading the platter, arm, and cartridge, and when I wanted that final "push over the edge" (as Nigel Tufnel would say) I purchased the SDS. I can't say it made my table sound like a brand new, SOTA, $10k+ system, but it did make the noticeable improvements noted by Rushton above.