invented twice - both post war the second (the one you see around today) was a development of the first to make it easier (+ cheaper) to produce as well as seeming less 'cluttered' and more modern than first - there is a mention somewhere in Manx Life I think of the designer and her comments on it.

You are safe wearing it as the law that required redlegs to take first boat off Island or be treated as outlaws was repealed some 400+ years ago.

Mind you the whole kilt thing was an invention of the 18th century anyway though the highlanders did wear some form of plaided blanket for warmth - the Manx women also had their sunday best checks.