Heat sources

[tress29]

I've read that a lot of you rely on an under tank heat source for your hog. What is the primary difference in something like this Zoo Med UTH?

http://www.petsmart.com/product/index.jsp?productId=2752652

and something like this Exo Terra Substrate heater?

http://www.petsmart.com/product/index.jsp?productId=2752652

I'm not planning on setting up some huge rack in my 649 sq ft apartment or anything like that, so no reptile rooms and heat tape/rope!

Thanks for your input...

Theresa in Indy