Actually. it makes turn 10 hero power not crappy because you can just summon a 10/10 silver hand if you have no other plays
And the enemy then can sap/silence/kill it off with a spell. So you give him 2 for 1 value; that's not very good. But the hero-power are right, if the minion stays alive, then it actually can do a lot of damage. Still: Is this effect worth 8 mana and a deck slot? And here i have my doubts. Especially since it shares a deck slot with Lay on Hands.
This card is not to be underestimated. Can be a charge from hand with a low cost charger, can be a 10/10 swing from an existing board, can be a tempo play (attack into a minion for free then play this card on the injured card).