I had one when I used a two prong rest and it worked great. When you draw back the flipper flipps up and out of the way.
I have since gone to using a whisker biscuit and like that even better.

EDIT: sorry i see you are new to bowhunting so if you don't know what a whisker biscuit is here is a link
http://www.carolinaarcheryprod.com/