You will note on these types of measuring equipment they are only a spot check and must be calibrated prior to use.
At this time no one has managed to make a probe that is continuous use for permanent immersion in sea water!
Which is what they need to be to align with the profilux control.
And actually the Apex does have a salinity module. Price and usage wise more of a pain. But if you only have a profilux 3 model, then you also have to buy an additional conductivity card and probe.