You can blame my over-privileged (white privilege some might say :risas3
PNW dwelling self for that one! I don't know as much about rust as those guys do in the other parts of the U.S.
I'd always be more inclined to use it on a manual transmission for sure. I say that because my buddy had his manual transmission GTI parked on a hill and it managed to pop out of gear somehow and since he didn't have his e-brake on, it rolled down the hill and through someone's fence, into their yard!
I don't think you have to worry about automatics popping out of gear... I could be wrong.