I got one a couple of years ago. It will kill mice as well as rats. My experience was that it did pretty well when I first put it out but the effectiveness lessened over time. That was not because the number of rats and mice went down, I think they somewhat learned to avoid it. Possibly moving it around more would help with that.
Another issue was that I had to take it apart and clean it fairly often. The dust where it was would short it out, plus possibly some animal juices that needed cleaning.
It will kill mice and rats. Mine did not come close to eliminating them, if there is much of an infestation it just can't keep up with birth rate. It is a tool in the arsenal to try to keep the numbers under control, but it's only one tool. You need more.