Boss introduced by Browning in, I believe, September 1993. Boss has been reported to be capable of tuning barrel harmonics to improve accuracy, at least with factory ammo. This was the original intent of Boss before it was perforated to perform as a muzzle brake. There is some disagreement among users regarding effectiveness of the brake version as a harmonics tuner. Some folks have reported that handloading exceeds Boss capability. Like any muzzle attachment, there are reports that a Boss that is not secure adversely effects accuracy. Such result is apparently akin to cousin Robbie's ill-fitted custom muzzle brake on any rifle.
That's about all I know from first hand experience and inter-web search info gleaned when researching the year Boss was introduced.