I have killed a few birds over a strutter decoy, and I have "gobbled up" two. Both times birds were hung up and I gobbled as a last resort. One flew across a swamp and landed right in front of me, the other came running down a logging road looking for the intruder. Both were among the coolest hunts I've had, but its a rare situation for it to work. You have to catch one in just the right mood.
As for the decoys, there is absolute no logical way to argue that they don't work in the right situation. I never carry a strutter just to use in general, but I always keep it in my truck during season and if I am hunting a particular bird or particular group of birds that I think will come to it, I will absolutely use one and have had great results with it. If a bird seems to be a dominant bird and or when a turkey routinely struts in the same field, he will likely be offended if another bird is strutting a hundred yards away from his spot, and then a strutter is deadly.