I was burned in the early 80's by the S.G. vs Salinity comparisons so I am admittedly hypersensitive to it.
I started in the late 70's with what would be an archaic reef tank by today's standards. Not enough light, salt mixes that varied batch by batch, but the point is I use a Glass hydrometer and a salinity chart for several years with great success. That's all I had available and I still have that same hydrometer and it's still as accurate as my refractometer but only after referencing the chart with the tank temp.
The neatest thing was invented, the swing-arm hydrometer. I had heard about them but didn't get my hands on one until sometime early 80's as I recall. I found it to be really easy to use. After slowly killing most of my inverts (the fish were fine) I realized that the swing arm couldn't make the same measurement from one day to the next and was about as useful as testing the water with my finger. I just went back to the glass hydrometer and it wasn't until last year that I finally broke my glass beaker (to hold the water for the hydrometer) and bought a refractometer. WOW, what a great feeling to join the 21st century
Aquarium Pharmaceuticals claimed the swing-arm I purchased was auto temperature adjusting. I found that not to be true.
Have improvements been made to the swing-arm hydrometers?
My thrust here is that I believe hobbiests should be concerned about not using S.G. and Salinity interchangeably. Especially the newer hobbiests. I defer to your coral knowledge and how important salinity maintenance is for them. My specialty is tropical bugs, the ones that keep our marine microcosms functioning properly. In my world discussing Salinity solely in terms of water density doesn't cut it and is a good way to damage the critter populations of a successful reef.
I just used a real ****-head way of trying to get my point across at first.