Jojo, swing arms can work very well if they are properly calibrated, cleaned and the bubbles knocked off when reading. I have to shave some plastic off my swing arm to get it calibrated right, then it worked well. Refractometer is much easier to use though.
I had a bad experience with an ATO on the water container that got stuck and flooded my basement (through the floor) so I've been really leery about using one on the tank which is on a slab, but a carpeted slab with lots of real furniture in there.