HGE is very frightening - two years ago we woke one morning to bloody vomit and bloody feces all over the bedroom carpet, and Annie, our little terrier, lying on the floor in distress - she had made no noise at all. Wrapped her in a big towel and had her at the vet in 15 minutes - they told us she would probably not have survived many more hours. We had never heard of this before - thank goodness we're now aware of how serious it is.
I've been using one for about six months and it really does seem to help. I have a 13 y/o Jack Russell, and before the vest her whole body would shake terribly and she had very rapid panting. Of course she knows before I do when thunder is coming, so at her first sign of nervousness on goes the vest. My vet is selling a lot of them.