While trying to hit 500 PvP battles, I came across a few with Viper. The first was Rags team, I was like WTF!
I needed some ironite so I got the ironite/viper pack, $19.99. They are crazy good. I used Viper, Alchemy, Labrynth and Frontier (all 5 tali sets) on almost every team in Gauntlet, levels AA and above.
The counterstrike on the Vipers are 100%(despite what the description says.)
Great to buy, but we all know what happens when something works too good.
Enjoy them while we can.