I’ve never used a refractometer, some people hate the hydrometers but I personally like them. Way cheaper and once you know how to properly use it you’ll get a pretty accurate reading. If you have more delicate corals or fish definitely spend the extra money and get a refractometer but if you’re just setting up a new tank, it’ll do the job. YOU WILL NOT get an accurate reading if there are bubbles on the needle. Just gently tap the entire hydrometer on a flat surface a few times and the needle will adjust to the correct reading.