Most warlocks I have faced have used two Lashes. (One uses three, Im not even joking.)
I have -2 equipment (Flame hubrick I think?) and elemental cloak in every spell book I run.
Now, thats just playing the meta. There is the warlock or a wizard with fire to fight, and not much in the way of; Frost, wind, and to a lesser extent lightning as of right now... but all that will change shortly.
Lash Of hellfire is amazing...and its amazing for three things;The ring that gives a +1 to fire, burn and reach. If I could, I would choose LOH over the mage staff (For reach) any day. My flyers are not safe...my nature conjurations are not safe...my mage is not safe....with bear strength, gauntlets of strength, ring of fire, and the warlocks melee +1....you got 9 damage on a quick attack that can reach flyers and burn....AMAZING.