Take a look at this..........http://www.drycreekphoto.com/Learn/Calibration/MonitorCalibrationHardware.html
For high-end displays, many vendors offer their own pre-tuned colorimeter sensors. Our experience with a limited sample of such sensors (all X-Rite Eye-One Display 2 based) from HP and NEC has been good. The OEM calibration performed reduces the variability between units by half compared to a stock Eye-One Display, and greatly improves accuracy on the monitor it is tuned for. The drawback is that these customized sensors are only accurate for a single display type.
The new Pro seems to be significantly better than the older '2'.
The new sensor may be tweaked slightly but the big downside is that it's locked
such that it can only be used w/ Spectraview/NEC hardware/software.
Yes, I believe the new Pro is the best option but then again, if you're
using the Retina display for non-critical work, you may want to just save the $$ and not bother
calibratiing it but that is a personal decision.