Product review (5 stars): I couldn't be happier. Haven't had it for very long and it ...
I received a discount and was able to purchase this product for 13.99, it came on time and was exactly as advertised.
The build quality is solid, all metal casing and unit is slightly heavier (read: sturdy) than it looks.  I have tested it's accuracy with distilled water and against a beer that I knew the final gravity of and it is more accurate than my floating hydrometer (plus much easier to use.)
I am wasting less mash/beer and am able to get more accurate readings, I couldn't be happier.
Haven't had it for very long and it came properly adjusted so I haven't worked through a calibration yet,  but seems straight forward using the supplied small screw driver to adjust field depth.

If trying to think of a complaint, it would be that the included manual wasn't super clear or extensive.  I'd recommend watching a you tube video on using a refractometer if there is any confusion, I didn't run into any personally.