Product review (5 stars): I tested it! Mine works fine
I recently got mine and tested it using a 62% Boveda humidity pack in a plastic bag. Mine read 63%, which is a more than acceptable margin of error considering that, according to the box, it is rated to +/- 3% humidity. I have not rigorously tested the temperature measurement, but it seems accurate. I mostly need it for the humidity measurement.

Other than that, there isn't much to say about it. It is super tiny and lightweight, but is also seems like the LCD might be a little fragile, so I wouldn't drop it or knock it around too much. We will see how long the battery life is given that it only runs on a coin cell. The readings update fairly quickly, too; just to test, I breathed into the vent for the sensor a couple times, and the humidity jumped up to 80% or so for a few seconds, then slowly dropped back down over a minute or two. Good enough for my needs.