IMO, conductivity can be a better way to measure salinity than a refractometer. I use an Orion 128 to measure salinity in my reef, as well as limewater potency. It also reads temperature, which all conductivity meters should do to make proper temp corrections.
But I would not keep such a probe in the water 24/7 because anything growing (algae, etc) or being deposited between the electrodes (air bubble, detritus, etc) can lead to a false low reading.