Underwater heater & thermostat...?

Hello!
   What to you think about using an underwater heater with this device...

http://www.reptiledirect.com/index.a....ory=357

  It is a thermostat and I would like to use it to control the temperature of the underwater heater in my Viv. It seems like I could just turn the heater up all the way and adjust the external thermostst.

Thanks!