it is an amazing bit of kit.
yes, the muzzle flash can give your position away, but that doesnt bother me too much given the sites i play at and the way i play.
it is surprising how well it lights up white bbs.
i run it all the time on my tippmann, and just unscrew it from the barrel if i decide i want to be super sneaky.
i do have a mildly amusing tale regarding my bifrost....
i used it at apocalypse airsoft a couple of weeks after it got released (having ordered directly from acetech, i got it in my hands before any of the airsoft shops i use), as well as TAG rounds from the M320 mounted on my tippmann. one of the enemy players approached me in the safe zone as i was reloading the TAG shells and asked if i was the one with the rainbow tracer as well as the TAG rounds. when i confirmed that i was, this player told me that i had confirmed his fears and then revealed to me that some of the blue team had associated the TAGs and the rainbow flash... and that when they saw the muzzle flash, they turned and ran the opposite way.. so the bifrost can be used as a tool of intimidation in the right circumstances