RBI has a FAQ on their website about the difference between belly and back heat. For me, its a question of what the ambient temperature is in the room where the rack will be placed. Since I have a dedicated herp room that is usually 75 degrees in the daytime, I could use a back heated rack if I wanted to, its just that I never bought one. I'm not opposed to them, its just that I always bought belly heat since I moved a lot in the years before I bought my house and I never knew where my racks were going to end up.

FWIW, you will find a lot of people who like Helix Tstats. I bought three of them, and after having two fail on me, I gave away the third. I've never had a problem with Herpstats though.