I read somewhere that Butterfly Swords are not a Chinese weapon; but they are used by Lau Gar and Wing Chun. What do people think? Are they defensive or only offensive?

I have read in wikipedia that butterfly swords are sometimes called buterfly knives in english, but there is a confusion with the philippino balisong, also called butterfly knive :

see here :

http://en.wikipedia.org/wiki/Butterfly_sword
http://en.wikipedia.org/wiki/Butterfly_knife