RPT is not for radar but for camera based systems, RCT golf balls are for radar based systems.
RPT is short for Rapsodo Precision Technology. RPT-enabled golf balls feature a collection of markings (spots, really) on the cover that allow the MLM2PRO launch monitor to accurately capture spin and spin axis measurements. If that also helps on the R50 I don't know, suggest just try them out.
Yes, you are right. Didn't read right in the first place.
That said, I have used Rapsodo balls with black dots, and in my experience, they didn't improve data accuracy with the R50. If anything, the results were worse. The R50 relies on the dimples to capture spin data, and the large black dots may obscure those dimples more than is ideal. In my practice, standard golf balls consistently produce very good and realistic spin rate readings
