Should I keep my Iron Keys or use them before the update hits?

[MrSammy]

First, go see this guide by Kaya:
Troops leveling & Sacrifice 1.0.8

If you want more info on the traits and the troops, you should go see the Wiki:
Gems of War Wikia | Fandom

Then, as @Shimrra said, it depends if you want to traits or troops.

One way or another, you will be short of cards and traits… I had 3500+ iron keys and 500+ gold ones and 3000 gems, and I’m still far away from maxing all my troops, months after the update.