ExoTerra makes a Digital Thermometer and a Hydrometer. ( they also make a dual one with both). It mounts on the top of the lighting fixture and a probe is ran into the enclosure for readings.
Yes, that is only a Hydrometer. That one will only read humidity in %. It should already be calabreted and just needs to be turned on (usually there is a piece of plastic to be removed by the battery). And it's ready to go.
FYI , a "thermostat" as you stated in your title is something completely different than a thermometer or hydrometer . A thermostat Is A device that automatically regulates temperature, or that activates a device when the temperature reaches a certain point.
Hydrometers and thermometers only give readings of humidity and temperature .