Refractometer? I'm not sure what the benefit of this is over a hydrometer???
If you're a full volume wort brewer (unhopped Extract, or full blown AG) refractometers offer several huge benefits over a standard refractometer.
1. Sample size - when measuring gravity of liquid, you don't need to float your hydrometer in maybe 100+ml of liquid for it to work.
Literally 3 drops of the fluid is heaps.
2. Practicality - you can't just throw your hydrometer into your boiling wort in your kettle without the risk of it breaking and then ending up in your beer.
Just use a pipette, draw out enough for 3 drops and take a reading.
You can do this as many times as you like throughout the boil.
HOWEVER, refractometers aren't without disadvantages either.
The most common one by far, is that when measuring fluid that already contains alcohol, you need to use a conversion chart, which isn't hard at all once you get used to it.
I gave my hydro to a mate several years ago, and have switched exclusively to my refractometer. Absolutely love it.
By the way, if you use brewing software (like i and many others do) most programs have built in converters anyway so it really is very easy.