That rack is well-built. It uses heat tape appropriate for baby boids.
I think the ideal baby king rack uses a thin strip of heating cable rather than Flexwatt, but that is my opinion and doesn't mean you shouldn't get this rack. If you ever build a rack for kingsnake hatchlings, try heat cable, it rocks.
Temp controller usage: Place controller near rack where it is accessible to you. Place probe in proper location (see note below.) Plug heater into controller. Plug controller into 120V outlet. Set temperature. Pretty easy.
Probe placement: This is the most important aspect. Improper probe placement will yield bad results. For kings, I like a thin heater set to about 90 deg, but with Flexwatt and small boxes, that is too much heated area at 90 deg. So, I suggest using one box in the rack as the temp set box. Put in substrate just as if a kingsnake were being kept in it, and place the probe in the box over the heated end. Set for 82 I guess.
You can experiment with the probe placement. Some folks just tape it down on one of the shelves over the heated area right between adjacent boxes. Whatever works. Just don't overheat those babies.
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Mark