Two potential points of failure: the UTH could fail or the rheostat/thermostat could fail. It would really only appeal to someone with one snake, or to someone who needed just one enclosure for a specific purpose, like quarantine. Most thermostats can handle the electrical load for several UTH's.
You can find UTH/thermostat combo units under the brand name VIVOSUN on Amazon, but if you look at the price, purchasing one costs about the same as getting the UTH and thermostat separately.