I was quite surprised when I read the FAQ.
When reading though I am still not quite sure what they mean.
Q: The resource ability on Metalworking says, “When
playing a unit from hand, add 3 to the strength of its
attack.” What exactly does this mean?
A: This means that a player may use the resource ability before
playing a unit card in battle in order to have that unit deal 3
extra wounds if played into the same front as an enemy unit.
Thus, a strength 1 unit would deal 4 wounds to the enemy
unit in its front. The strength boost lasts for the entire battle,
making the unit harder to kill.
What if you play your units in a new front and use iron on metalworking? Does that count? Since it says "if played into the same front as an enemy unit".
Since they clearly specify that it makes the unit harder to kill, one must conclude that they also get health boost, which in my opinion is really overpowered to be a level 1 tech.
In my group we have decided it only counts towards the attack and not health.