a refractometer is a very precise equipment, for me tech junkie, it is the best (analog) toy you can buy... but for salinity meter, ph etc you need to recalibrate once in a while... so anything with a probe needs recalibrate at leat once every 3 month... conductivity meter?? i cannot compare salinity measure eqquipment with this... so i cannot help you with that one.
as for bang for the buck, out of the three i will buy refractometer... ( opinionated).
for myself, i will buy a aquadyne/neptune contoller
and a refractometer. that is the best bang for the buck.
