Rock Bottom Airsoft does a comprehensive review of the Bocca Tracer Unit from Nuprol... "In this video we take a look at an affordable Tracer unit for your Airsoft replicas. Including a test fire using it in low light conditions.

Tracer units look cool as an accessory but really come into their own in low light play. Indoor CQB or night games can certainly benefit from a Tracer unit. They allow you to track your shots as well as looking awesome.