First try: can't actually do it from Linux Chrome, has to be Windows/Mac/Chromebook.
Second try, on Windows: Extension downloads the image. Windows asks if I want to allow Chrome to make system changes. Then Chrome crashes.
Third try, on the same machine: The exact same image is downloaded again. The progress bar for unpacking the image goes to 250%, and -15 seconds remaining. Writing the USB stick finally works.
The extension is able to write raw data to a USB device, which seems like rather privileged hardware access. But there is nothing in the permissions section of the extension suggesting there is anything special about it. That seems really strange.
(It was just creating the image that was odd. Once that was done, everything was smooth on a Windows 8-era Samsung laptop.)