ORB allows for a cleaner and tighter looking assembly. The thread pitch is the same as the JIC/AN fittings. A -6 JIC/AN male fitting is the same as a -6 ORB

Using ORB instead of NPT keeps you from using thread sealant since they are straight threads and the o-ring provides the seal. Any mfg that sells ORB fittings will fit and work without issue into a ORB port of the same size.