PD 39 X
The PD39X has two absolute range sensors inside and the pressure difference is calculated with the device firmware. A low differential pressure measurement will be degraded if compared to the PD33X because it represents small proportion of the sensor range and the uncertainties of two sensors are being combined. However the sensor is well protected if you accidentally apply 300 bar to one side only, for example if one of the pressure fittings leak. The DP accuracy for a 300 bar range PD39X will be 150 mbar.
PD 33 X
The PD33X has a 200 bar line pressure rating as standard, however you cannot apply full line pressure on one side, it must be on both sides at all times, otherwise the diaphragm overpressure rating will be exceeded. This sensor will provide the best accuracy at 0.5 mbar for a 1 bar dp range.