I have both Tracer unit styles. The TM Tracer unit (V.2) is by far better IMHO than the Madbull Hopup tracer. The TM version will work in dim lighting situations as well as dark or night situations. The Madbull Hopup is OK to fair in dim lit areas (the front "office style" area of XT) in dark areas it works well (the dark "black light" area of XT). My preferance would be the TM Tracer unit only because it works in both dim and dark lit areas and for the simple logic of you get what you pay for. The TM unit may be pricer but works, where as the Madbull version works but only in dark situations.
As for BB's no lighter than .20 please .28 would be very nice. For colors red and green are fairly standard.
Here's some Night games from the US where they had all tracer units.
YouTube- Airsoft Night Ambush and Attack with Tracers by Utahs Premier Airsoft Community Black ops Elite.
YouTube- B.o.E Combat Airsoft Night Operations April 25th 2009