Hmm... Warlock doesn't even need to have armor to give him 2 nades. Sun Singer already gives him that. Then Voidfang Vestements boosts Axion Bolt Grenades (one extra axion bolt is pretty handy and I think they last longer than usual too, I have seen my bolts pursue enemies welll after I was killed) and you always spawn with grenade energy, so even if you use this armor with Sun Singer with the double grenade it means you spawn with 2 grenades. Lets you carry more special ammo... Just depends on how you configure your character.