“You can boost its effectiveness somewhat by mounting a piece of styreme foam insulation (Home Depot 2x4' sheet is like $3.00.. cut with big scissors) between the heater and ceiling.” -markg
Hi Eric - Even more effective might be to mount a piece of foil-wrapped insulation to the ceiling before mounting the heater. Guess it depends on how tacky you want the cage to look 
It never seems to fail with me – when I try to save a few bucks by buying something a step or two down from what I really wanted, I end up dissatisfied, or messing around endlessly trying to make it work. And I often buy something to replace it down the road, anyway, so I don’t really save the money.
With some of my smaller cages, like 2' wide, I’ve considered mounting an Ultratherm heat pad to the ceiling. Given my ambient conditions, I know they would heat the cage effectively, but the prospect of sealing the edges effectively so that a snake couldn't crawl behind it turned me off the idea.
I’m not knocking the Desert Rays brand specifically, but as I think Mark implied above, if you want a heat panel, buy a heat panel; if you want a UTH, buy a UTH. But no, they most assuredly won’t “burst into flames.”
-Joan