I used one during one season in Colorado. Personally, I am not saying it doesn't work, but I tend to like making the elk look for the elk that they heard calling.

I can recall twice where we had the Montana Decoy set up. the bull came in, but then locked up about 60 yards out. Not that it was the decoys fault, in both cases the bulls focused on the decoy, but if you watch the video below, I have had better luck making them search for what they heard.

I personally don't carry one anymore.

http://s126.photobucket.com/albums/p113/rob1dr/?action=view&current=ElkClip.flv