I know of many who use it and say it works. However I also think a doe bleat is the easiest call to mimic with your own voice. Basically it is a BAHHHH AHHH (like a sheep but more groany).

As far as usage rut is the intend, but late pre-rut and early post rut may get the bucks goat a bit on one last kick or first kick at "THE CAN"....sorry bad pun!

The bleat in all honesty really hasn't work that well, with the exception of a buck in love mood and grunt didn't stop him for me. So it has been useful, but I do it with my mouth instead.