The times ive used it, be it under tank heaters, or 3" flex, i did not like it, or had problems with it. In the time i have been using back heat specifically, i have had zero problems with it, and feel it provides a more even gentle *consistant* temp gradiant. even on the bottom of a rack * which is always a little cooler*
Actually, 3" belly heat burned on me. It does not work in a cooler climate. and had one heck of a time keeping the temps where i wanted them.
http://pics.livejournal.com/mooingtricycle/pic/0006q0h6
Ill never use it again. * though i would consider 11" belly heat, but that would mean dismantling my racks to do so. and honestly. It aint worth it.