That's what I figured you meant: that is a UTH controlled by a rheostat...it's not accurate, you cannot control the heat to a certain temp. with it...all you can do is
install it & let it run for a while, then keep checking back as to what temp. it's actually producing in the cage, and making adjustments to get as close as you can to
what is needed. Thermostats actually control the power to the UTH they control, either by proportionally reducing the power, or by making it go on & off to achieve
the right temps. which are read by a connected probe. So this (above) is better than nothing, but not the optimal or the safest choice.
One difference is that as your room temperature changes, a thermostat is going to adjust the temps produced, whereas that rheostat is going to stay where-
ever you dialed it, which might end up being too cold or too hot. Also, if there are power fluctuations, a rheostat may not adapt.