this is better than flashy shot IMO. only 5 min. cooldown, and it does help keep hate off you when you need to. and yes this does stack with flashy shot.
flashy shot doesn't "get the fight over with faster" because it doesn't help that much for exp. mobs. they're only 3-5 levels higher than you. so that's like 10~20 HP per level difference (i'm ball parking that, but i know it isn't much because i still didn't see much increase when i used it on mamool ja's).
only question i have is...if this is double or triple meritted, does it drop 10 enmity per increase? if so, you can almost do sidewinder + barrage + stealth shot/sidewinder and what's the point cause after that mob should be goners...