personally I dont have faith in the rattle bags, experience has proven to me that real horns work best. Yes, the movement is a factor, but the sound is all it's own. Never used a vanilla cover.
I agree, them pissy little rattle bags don't sound anything like the real deal. You need a set or big antlers to do the job. Here in Kansas ratteling hard is working good now.
I have used a rattle bag for 3 yrs now, last year I rattled in my 12pt I shot, this year I rattled in 2 small 8 pointers, it is not something I always use, but it is there just in case!