I am on the negative side of this card. I feel as though the card does very little to the game state. There is constant mention of putting this card on a very strong ally of strength 3 but all that you are doing is adding a small amount of damage or actually reducing the damage that the character dishes out over the course of the game.
I don't want to bring into discussion Hulk at the start because of the randomness he has, but let's look at any other generic character. If you have a 3 health ally with 2 attack power, you will get 2 attacks out of the ally for a total of 8 damage. They are doing 2 to themselves while dishing out 4 damage (2 base + 2 from enrage) on the first swing, followed by another follow-up attack that would do 4 damage.
If that ally were to not be enraged he would attack three times. Therefore you would have gotten 6 damage out of that 2 damage ally anyway. So you really only netted 2 damage. A card for 2 damage is not a "good card", it's average and it really only works that way if you found it when your ally was fresh. It actually gets worse with higher attack allies because you are robbing them of their damage they could have done.
A 3 damage ally over three turns would only net 1 damage since you would dish out 9 normally but would swing twice for 5 with this attachment dealing 10. And if you have lots of icons in a Hulk deck and can maximize 5 damage from Hulk, you are losing damage. Hulk alone with 5 damage per turn with a icon would do 25 damage (5x5). If he has the attachment on he only does 21 damage (3+2+2 x 3 uses). You do the damage slightly faster, but you do less.
I actually think that this card is a bad card, and your deck slots would be better spent on something else. These numbers get worse of course with even health allies, but I wanted to provide the benefit of the doubt of playing this on an odd-health ally.