Tether Kill Switch

Bike bandit has a tether kill switch for $29.99. Any body have experience or suggestion with where to get one for a decent price? $30 seems reasonable.
The track here requires one for bikes that exceed 120mph, I faked one last time and should probably get on for real. I also need to look at the diagram to see if the kill switch is NO or NC.

Below is the tether switch I was looking at ....

Parts Unlimited Tether Kill Switch - BikeBandit.com

From the huge response I take it not too many here have much experience with one. LOL
Maybe you could ask your kids about it for me?