Hydrometers are notoriously inaccurate. Refractometers are the way to go. Just an FYI, calibrate it before EVERY SINGLE USE. Label the most accurate of the hydrometers reading after comparing to the refractometer and note that as the correct level. JIC the refractometer breaks.
Swing arm hydrometers are not great as you have discovered. The glass bobber type are considerably better (better than a refractometer even since they require no calibration). The down side of course is that they can be fragile so you need to handle them carefully.
I use an Instant Ocean hydrometer, its right with my LFS when they checked my water with a refractometer. When Marine Depot had the big sale, I picked up a Coralife hydrometer to have a back up. Well its way off, my Instant Ocean reads 1.025 and Coralife reads 1.028