Free: Contests & Raffles.
After calling guy after guy using a cow elk call in a bull only area, I would not use a decoy for fear of being shot. that's just my two cents, however if you have access to private land I would use them in a heart beat.
I own and use two decoys. The first will "always" be on my bow, they work and work very well. http://www.poisonarrowgear.com/ The second is also a great tool in my elk kit but is deployed a bit more as the hunt dictates (I sometimes use the cow behind decoy slip and sometimes the camo slip). Plus, it's a great walking stick! http://elkmtngear.com/
The umbrella seems like one more thing to worry about in the woods but would be interested in others who have tried it.The clip on cow to my bow is interesting, and I see the potential benefit but the height of the brush would have to be conducive otherwise it will appear like a floating head with two camo legs behind it. Again, would be interested in any consumer successes for those willing to share.