No. The product in this case relies on unintended functionality in a specific firmware version of an Apple device that is specifically designed to not be suitable for this application. In this case it is the add-on device that is not offering refunds if it stops working.
Where do you get the idea that Apple specifically designed the AirTag to not be suitable for a third party device to control when it switches on and off? I can understand how they might not approve of this adaptation to their product but I don't see any reason to believe they specifically designed against it.
Yes.
> if it stops working.
It doesn't magically stop working though, it would be apple explicitly putting in effort to break this functionality and forcing you to update a device you own, forcing you to use it only how they want you to use it.