My guess is that the margin of safety on the Butane cannisters is adequate.
The safety of
butane canisters is most definitely adequate. On butane. Put 100%
propane in that same canister, and you're very likely to have some serious problems.
I have not heard of one blowing up inside a hot car in the desert.
Yes, but again, those are properly filled with a
butane blend. This guy is selling a device which fills with
propane.
Tell you what, buy the device, put it in a hot car in the sun on a hot day, and stand WAAAY back with a camera. When you've the video posted on YouTube, let me know.

HJ