I have a Hanna digital unit going on 4-5 years now...LOVE IT !
You should avoid all hydrometers and go right to refractometers I you don't want to drop close to $200 ...
I just figured salinity is the most common test so I wanted to make certain I got it right and it was easy and accurate every time.. Probably over kill for the level of attention I give my marine..But it is easy and accurate..
1 drop 0 TDS water to calibrate /1 drop of salt mix and done...15 seconds tops..Digital read out ,no guessing .
I mix 24 hours in advance in a brute 32 g barrel with power head..