My response to the invisibility question (I know it is not mine to answer -but my response made me laugh at myself) was - how can I go do something naughty if I don't know how long the invisibility will last. What if I become visible in the middle of it? What if it wore off in rain or etc. So first I would have to ensure it would stick or that I had control over it. Then I could do something that depended upon me being invisible.