Rob,
I can't answer question #1 since I have little experience with any manufactured cage, much less the large ones.
The oil-filled, radiator style heaters are as safe as a choice as you have with plug in heating. And they are remarkably efficient.
For peace of mind you might want to run the heater through an aftermarket thermostat like a Ranco or Johnson Controls.
I used to use these heaters exclusively and still have one as my backup system in my snake room. I pick a cool weekend when I'm home and fiddle with the built in heat control until it's keeping things slightly warmer than my desired temperatures. Then I hook up my aftermarket thermostat and set it for my desired temperatures. This approach is similar to a double thermostat.
I'm sure you can set up your herp room in a way that heats your burms but also keeps the sand boas a bit cooler. Buy and infrared thermometer and play around with cage placement, etc. until you get things right.
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Current snakes:
0.0.1 Gonyosoma oxycephala - Java locale (green)
1.2 Gonyosoma oxycephala - Jave local (green)
2.2 Gonyosoma janseni - Seleyar locale (all black)
1.2 Gonyosoma janseni - Celebes locale (Black & Tan)