There's no hidden motive here. It's interesting work, but usually this type of research is done on malware samples and the like, and not "regular" apps. That's why I'm curious if the authors should fear legal ramifications, and if so why (or why not).
I'm mainly interested in answers for the US, Germany/EU, and Switzerland.
It doesn't feel like you're curious for your own sake. Why are you asking?
Also, anything is illegal somewhere. Where do you want the answer to apply to?