I recently purchased a Park Tool TS-2.2P wheel truing stand. Since I'd read some reviews about buyers receiving the stand in a poor state of calibration, I purchased this centering gauge at the same time. I'm glad that I did. I'll quote from my review of the stand the stand was way, way, way out of proper calibration. It didn't seem to me that anyone at the factory had even tried to calibrate it (or inspect it for quality assurance). Without the centering gauge, this truing stand would have been a very expensive and awkwardly shaped paper weight.
This centering gauge makes it easy to see whether the stand is properly calibrated. The nature of the stand requires a lot of two steps forward, one step back adjustments to get it properly calibrated, so I won't say that this gauge makes it easy to get it calibrated, but if you're patient, it will help you get the job done and be confident in the result.
It's pricey, but it's a hefty chunk of metal, and it seems like it's precision-machined and built to last.