All standard jokes on tracers aside

(Via one of my Intertubz Spy Network)

They sell it as a trajectory identification aide.  BS.  It's for making nighttime at the range look like a Star Wars battle scene.

The plus about this particular brand is that it's "cold"--it's no more likely than standard ammo to set something on fire.  It's imperfect--you can't see it in daylight--but on a heavily overcast day, or at an indoor range, you're going to be able to identify whatever shooting problem ails you--in 9mm or .45 ACP, at any rate.