Product review (5 stars): It's awesome.
uses the sensirion sht75 sensor- which is by far the best I've used. It's FAST to respond to humidity and temperature- on the order of a fraction of a second, so you don't have to wait for it to update its reading.

I've seen the sensor alone go for about $40, so this is a deal.

Battery life is surprisingly good (can go more than 24 hours).

Only quibble is that the bottom is round so that you can't actually stand it up like in the picture.