I'm curious if you're still using these and what you think now a year later. We recently purchased two of the 11x40 ones to use in brooder boxes out in our unheated chicken coop. We had 10 chicks hatch last week and we moved them out to the coop Friday morning. I checked on them just about every hour throughout the day, and they seemed more or less fine: they were grouped together under the heater but they weren't noisy and they weren't shivering or panting. But Saturday morning 8 were dead and a few hours later the other two died as wellI'm devastated and trying to figure out what happened since we have 42 more eggs in an incubator set to hatch in two weeks.
Have you ever been able to get a temp reading under the heater? My husband used both an instant read meat thermometer and an infrared thermometer and while the surface temp of the Sweeter Heater was around 160, nothing under it ever measured above 60. I think the chicks froze to death but I am stumped as to why. All of my research suggested this would be the solution we had been looking for and it clearly wasn't.
We are now considering the Mama Heating Pad solution others have posted on here, at least until we can figure out these Sweeter Heaters. We may just return them though because you're right, they are not cheap!
Oh, that's awful! I'm so sorry your chicks died.

I haven't used the Sweeter Heaters since last year's hatches, but when I used them last year, they worked fine. I never tried to get a temperature reading under them, as several folks had commented that this is difficult to do accurately with a thermal panel. I went by the chicks' reactions.
It's really hard to know what went wrong without being there, but here are some questions to consider: How high was the lens of the heater panel above the litter? Was there an area in the brooder box that was not covered by the heat panel at all (a cooler area where chicks could go to eat, drink and mill around)? Did you turn on the heater several hours before putting the chicks outside to heat up the litter? Was the heater set up against a wall so that heat could be trapped under a portion of it? Was the brooder free of floor drafts?