Product review (5 stars): Accurate, economical.  Good for use in Incubator.
I've now purchased three of these.  They are accurate, not only to each other, but to other devices when calibrated.  (If you want to calibrate it, or test the accuracy, google "salt humidity calibration").  In case it was not accurate, you can adjust it with an offset in the controller.

The controller comes pre-wired with the thermocouple and the humidity sensor already wired to the back.  They both extend to the same length of about 4 feet.  The temperature sensor is needed because it is necessary information to calculate relative humidity... the humidity sensor can't do it by itself.

I used this to control humidity in an incubator.  I actually use it to power a tiny humidifier, and it works great.  The resolution is to 0.1%, and you can see it rise point by point quickly as the humidifier comes on, cutting power to it at the designated cut-off.  You can also switch modes in the controller to run a de-humidifier (this is the default).  Controls are easy to change, easy to set up and the instructions are clear.

The light display on this is a bit brighter than the temperature controller of the same form factor sold under many different brand names.

If you change temperature quickly... like opening the incubator, and drop 20 degrees F in a few seconds, the humidifier will show zero percent (zero humidity) until the other sensor can catch up.  This is not a malfunction, just latency between the two sensors.  This shouldn't be a problem for almost all applications.

I've heard from others that it might not be as accurate high (>90%) and low (<10%) humidity levels, but haven't tested in these ranges.

I hope you found this review helpful.  Post a question if you have one... I'm pretty good at answering via Amazon questions.