Are metal horseshoe nails an acceptable method of securing electrical cables?
Metal staples have been around a long time, and haven't caused enough problems to be banned. So for as long as they're an "approved" method of securing cables, there is no problem using them.

Most of the inspectors in my area dislike them, since from time to time they're tacked down too tight by installers. If installed incorrectly they can indeed damage the cable, but in my experience this seems to be rare.