While I'm not a fan of the swingarm hydrometer, if not calibrated periodically, a refractometer can also easily give you false readings. They are delicate & I find mine creeps off calibration fairly easily. I've used my refractometer to calibrate the swingarm hydrometers I have, so they're just as accurate provided I go by the marks I put on them after comparing with refracto.
Not sure why the floating glass type hydrometer is not used or offered for sale in our hobby very much either. They can be quite accurate, the only thing you need to be aware of with these is temperature compensation. I wish I still had mine, but broke it some time ago. I still have a larger floating glass hydrometer for beer & wine making. I've used that to measure tank water as well, out of curiosity, and it was bang on with refracto reading.
Posted these photos before, but here they are again. Comparison of 2 swingarm hydrometers & floating glass. If I recall correctly, the refractometer reading was 1.025. The floating glass was pretty much bang on.
Coralife, 3 points low
IO Deep Six, better but 1.5 points low
Floating Glass, on the money
So yeah, based on my personal experience, by all means get a refractometer, it's a good investment. Floating glass will also serve you well at a fraction of the cost. Both are delicate, the refracto needs calibration, the floating glass does not, but needs temperature compensation. Most floating glass are factory calibrated to provide an accurate reading at a given temperature, which is not that far off the temperature we run our tank water at. They will usually come with compensation chart and a few degrees difference does not affect the reading that much.