I give the blue one from Premium Aquatics a 9.
I had to take off a point because of a scatch near the prism assembly and some wear on the daylight plate.
Otherwise, it was easy to calibrate, mine was only off by a hair, and just COOL.
My first reading says my water is 1.025.
My Deep Six Hydrometer says 1.023.
Hmm...
No matter where the truth lies, this refractometer is a lot easier to use than a needle float hydrometer, so I give it a big thumbs up! [smiley=thumbs_up1.gif]