I'm not sure I see how one of these antennae would help. I mean, wouldn't it just flex with the string and still cut you and knock you off the bike before it finally cuts the string? Anyone know of any actual case where one of these things actually helped?

wind screen
 

In Nov/Dec 2012, I rode through Brazil for over a month. A short ride to Boa Vista from Venezuela, then on to Guyana. The longer portion of the trip was from French Guiana, roughly across the north, then down the Atlanta coast. I remember seeing these pipa cutters mounted on bikes and wondered what the devices were design to do. Now I know. Personally, I never encountered kite strings crossing the road. More common are unofficial "toll booths", seen in various countries, operated usually by kids holding a rope across the road. The rope always gets dropped when you don't slow down.

If I were to go back to Brazil, would I get a string protector? I doubt it. My F800GS has a large after market wind screen, which would greatly reduce the chances of kite string catching my neck. Sure, a string could slide over the wind screen, down my full face helmet and do damage...I guess.