Besides the mediocre Vision Bonus that Flare provides there is a damage amplification part.
25% Bonus Damage and 65% armor reduction.
Damage than calculates as follows: (Attackdamage*1.25)-(armor*.35)
thus its only of limited use against zombies(Bolt gun gets to one shot them now) and other 0 armor enemies with low-ish health.
unfortunately it doesnt let weapons one shot reapers(30 HP, 8armor) that couldnt before, but two shotting them with good attack speed weapons works, such as Machine gun, uzi, Grenade launcher Gatling gun.
Those weapons work against Soldiers(150 HP, 7 armor) and Creepers(85HP,8armor) too.