Do decoys work? It seems that a big part of the answer depends upon how visible they are to a coyote. Dunno what terrain and vegetation you hunt in, but set up something the size of a decoy, in the spot where you'd be inclined to use a REAL decoy, and then get out there a ways on your hands and knees at coyote level and see how visible it is and from where it is visible or not visible.
Things can happen very fast when a coyote is close to you. I believe there's a significant benefit to using SOMETHING that will entice the coyotes eyes away from you, so you can move a little bit and line up a good shot without the coyote noticing your movement. But, you usually can't get away with very much movement; their periferal vision seems terrific.
I use an old piece of light-colored fur, about 2 inches wide and 12 or 15 inches long, tied on one end with a chunk of fish line to brush 2 or 3 feet above or to the side of the e-caller, where the wind will move it around. Sometimes a coyote will see it, stop, look, and study it just long enough for an easy, well-placed shot. I've yet to have one charge in fast and grab the fur; they seem to want to look it over first. But, just in case, I carry a second piece of fur in my pocket!
Have fun experimenting/learning.