The UTH on its own canNOT be controlled. That is what a thermostat is for. Just as you have one in your home to control the heat through the vents or what have you.
Different thermostats work in different ways. That one in the link (the Jumpstart brand) turns on and off to hover around the temperature you have it set at. For example, if you set it at 85F it will hover between about 83.5F and 86.5F.
Herpstats are an awesome brand I hear. They don't just turn on and off, but maintain the heat at the specified temperature. However they do cost a pretty penny...
I use the Jumpstarts, as do many others on this forum. I personally think they are great. If you've just got one or a couple of snakes, they work well - especially considering the price!
Sometimes people also use rheostats (a.k.a. lamp dimmers), but these are testy... they do not maintain a temperature, but rather dim the output from the UTH. The problem with these is that depending on the dimmer, they won't dim ENOUGH! So the UTH on its own can get above 120F - which WILL BURN YOUR SNAKE. You want the UTH to be about 85F for corns. A dimmer may only get it down to 100F give or take. It completely depends, not to mention that if the room temperature changes at all, so will the temperature of the UTH when using a dimmer. You have to constantly make sure it is where it needs to be, IF you can get it down to 85F.
Which is why thermostats are strongly suggested

I tried the rheostat/dimmer with no luck when I first got my corn. It's much less hassle, in my opinion, to get the right equipment from the get-go.