Question to Riot: About Custom Map Skins (Wooxy)

This is a fantastic third party program that allows players to change the look of League maps, but I have to ask directly and w/o any mistake:

Is this program legal to use?

I don't want to find out later that I was doing something I shouldn't have. Just to know, if I shouldn't be using this to just get rid of it asap.

Thank you for your time!